Information Sheet- North West Coastal Groundwater
Background
There is potential to develop new groundwater schemes on the western side of the Gnangara Mound System from the superficial and confined aquifers. This water currently drains to the Indian Ocean. The schemes would be in the vicinity of Perth’s North West Corridor and would develop with planned urban expansion identified in the Perth Regional Planning Scheme.
The scheme would require treatment Plants at both Eglinton and Yanchep.
The Eglinton groundwater treatment plant would receive water from the Eglinton borefield and meet demand growth in that area. Some water could be available for transfer into other parts the IWSS water grid, particularly in the initial years of development.
The planned Yanchep scheme would replace the existing local schemes that provide water to the Yanchep and Two Rocks communities. The planned Yanchep groundwater treatment plant would receive water from new borefields in the Yanchep and Two Rocks areas as well as be the receiving point for water from the Barragoon borefield. The proposed Barragoon borefield extends further north than the current extent of planned urban development. In this area, bore locations could be constrained due to limited road access.
The schemes have the potential to provide a significant additional groundwater resource for the water grid. The timing of development should be very closely aligned with the timing and nature of urban development within the north west corridor. Significant social and financial issues are expected to arise if implementation is attempted prior to land development.
There may be wetlands and vegetation that could be impacted by abstraction from the superficial or confined aquifers accessed by these schemes. The drawdown impact in the superficial aquifer is anticipated to be less than in other areas as these schemes will intercept flows that would otherwise be discharged to the ocean through Tamala limestone. Tamala limestone is known to be a habitat for stygofauna – microscopic aquatic invertebrates that can live in groundwater. This environmental issue would need to be considered prior to any development of groundwater in this area.
Current Situation
The Department of Water is developing a local area model to provide hydrogeological information linking the impacts of abstraction from the confined and superficial aquifers. Modelling would also highlight any impact on local wetlands and stygofauna. The source is also included in the Gnangara groundwater management plan currently being drafted by the Department.
These schemes are part of the Gnangara groundwater system and are being considered as part of the Gnangara Sustainability Strategy. This Strategy is currently being developed by the State Government and is being led by the Department of Water. It is due for completion in 2009.
Sustainability Considerations - addressed in planning
Economic | Social and Cultural | Environmental |
| Low cost local water source. | Limited source protection available. | Potential for impact on wetlands and stygofauna. |
| Most economically developed together with urban expansion. | Infrastructure could constrain land development if constructed ahead of subdivision. | Needs to be considered as part of the Gnangara Mound. |
| Water quality may be adversely affected by horticultural activities located close to borefields. | Low energy intensive source. |
Potential source yield
Current yield estimates for each borefield are
- Eglinton, 17 gigalitres a year
- Yanchep-Two Rocks combined with Barragoon, 33 gigalitres a year.
The total potential source yield is therefore estimated to be up to 50 gigalitres per year – enough for 200,000 households. This is subject to future water allocation planning.
Potential cost
Groundwater from these schemes for meeting local development is estimated to cost less than $1 a kilolitre. An additional cost associated with infrastructure to transfer water into the water grid is estimated to increase cost to $1- $2 a kilolitre.
The Future
The Gnangara Land Use and Water Management Strategy and the Perth Coastal Underground Water Pollution Control Area currently exist to provide source protection for these schemes. However, due to planned urbanisation of land over most of these groundwater resources there is a risk of potential groundwater contamination. Source monitoring and treatment will be required to manage this risk.
Water from these aquifers will require treatment and the full extent of treatment requirements will not be known until further investigative drilling is undertaken. However, it is unlikely that treatment issues alone would initially constrain source development opportunities.
The water quality at the Eglinton scheme could be adversely affected by potential development of a horticultural precinct at Carabooda through leaching of nutrients and pesticides into the water table. Over time, this may impact water quality and require the premature closure of this borefield.
Significant work is required to understand and consider other technical, social and environmental issues.
Key
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Potential source yield (in 50 year planning horizon)
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Potential cost (2007 $)