Gnarabup wastewater planning
Project goal:
We are undertaking wastewater planning for Gnarabup to ensure we can cater for future demand.
Status:
In planning
Delivery Date:
NA
What's happening?
Water Corporation is looking at its wastewater planning for Gnarabup, to meet future demand.
The Gnarabup Wastewater Treatment Plant (WWTP) currently treats the community's wastewater. Based on existing population forecasts, this plant can safely treat wastewater for the next decade. After that, we will need a higher capacity scheme.
An upgrade to the local wastewater scheme will be needed sooner if the wastewater volume is expected to rise a lot, in a short period of time.
We are working with the State Government on planning upgrade options for the wastewater scheme - if the Margaret River Resort and Village development, at Gnarabup, goes ahead.
The planning work will assess the viability of upgrade options, if needed.
What planning work has been completed?
We have assessed:
- Upgrading the existing WWTP capacity.
- Upgrade pumping facilities and constructing a pipeline to send wastewater to the Margaret River Water Resource Recovery Facility (WRRF) for treatment.
Option 2 is our preferred option - based on environmental factors, heritage and cultural considerations, community feedback and treatment needs.
During an upgrade, Water Corporation may need to truck wastewater from Gnarabup WWTP to Margaret River WRRF in the summer peak period. This is when inflows might exceed treatment capacity.
Trucking will occur only until we finalise a permanent solution.
What investigations have been completed?
We started early surveys because wastewater planning takes a long time.
The surveys included flora, fauna, and Aboriginal Heritage, in November 2021 and January 2022. Further surveys and geotechnical investigations took place from July 2024 to January 2025.
The survey area had no signs of threatened plants or major cultural heritage findings. However, some protected fauna species were identified.
The survey results will help us assess the upgrade options, especially the viability of option 2. It also helps to plan any upgrade to reduce disruption to these species and the environment.
When will Water Corporation decide which option to move forward with?
A decision to upgrade the Gnarabup wastewater scheme will occur when the wastewater demand forecast increases above the plant’s current capacity.
Planning wastewater upgrades takes time. We will continue investigating the viability of Option 2, should an upgrade be needed in the future.
Water Corporation is reviewing scheme planning for wastewater for Gnarabup to ensure we can cater for future demand. We are working with the State Government on evaluating potential options for the wastewater scheme.
We have received questions from the community surrounding this work. Here is additional information to answer some of your enquiries.
We plan wastewater treatment capacity upgrades based on the latest population forecast data* and operational lifespan. The current wastewater treatment plan (WWTP) is adequate until 2030 based on normal development activity within Gnarabup.
A decision to make changes to the operations of the wastewater scheme will be considered if there are any significant changes within the are causing an increase in wastewater volumes. The planning work we are completing is assessing the viability of options available if this is required. However, these timelines can be pushed back if wastewater volumes are below forecasts.
A project will only be activated once development is certain and funding requirements have been determined and therefore, a forecast delivery timeframe will be established.
*Historical Australian Bureau of Statistics data and location specific projection data is considered in establishing a forecast for a town. Potential tourist/visitor developments are also considered. Based on this information, residential growth in the area is expected to continue.
Gnarabup WWTP meets strict conditions under its environmental licence with Department of Water and Environmental Regulation (DWER).
We undertake thorough environmental monitoring to comply with all the conditions of our operating licence. This includes monitoring bores to review groundwater quality upstream and downstream of the plant and this data is reported to DWER annually. DWER has reviewed the site and approved its operation until 2023.
The treated wastewater is disposed of via infiltration beds. These are large ponds where treated wastewater is stored and either evaporated or infiltrated into the ground, similar to stormwater ponds.
Prevelly currently does not have reticulated sewerage and we have no plans to undertake infill sewerage in the area.
The 'infill sewerage program' was a State Government initiative to extend wastewater networks to areas where the presence of septic tanks posed a risk to public health, drinking water supplies and the environment. Under this program, more than 100,000 septic tanks in high-risk areas were decommissioned at a total cost of $1.2 billion.
All priority areas as determined by public health and environmental risk factors have been connected to wastewater schemes and there are no further infill sewerage projects.
Should landowners want a reticulated wastewater scheme, they could establish a contribution scheme whereby benefitted landowners could share the cost of providing the necessary infrastructure.
The proposed future options (WWTP upgrade and conveyances) are sized to cater for the potential additional flow from infill sewerage.
There are infrastructure headworks, connection costs and connection fees involved for customers wanting to connect to a wastewater scheme.
Emma Halligan - Community Engagement Specialist