City of Mandurah

When addressing our city’s growing population and demands for more open green spaces, we needed to consider its impact on our groundwater use.

Initial water supply upgrades to the Halls Head Recycled Water Scheme provided us with recycled water from the Halls Head Water Resource Recovery Plant (WRRP). Recycled water is sent to onsite infiltration basins underneath the WRRP, where the local shallow groundwater is continually recharged.

Initially, this water was being stored in 2 tanks and used to irrigate 4 of our local parks. However, further works led to the additional water supply to a major sporting oval in Halls Head, known as Merlin Reserve and South Halls Head Primary School ovals.

Our challenge was expanding on this to keep more public open spaces green and further reduce our reliance on groundwater.

Halls Head recycled water scheme limitations

While the established scheme was supplying treated recycled water for irrigation, there were some challenges.

The 2 production bores responsible for pumping the recycled water from the aquifer into the storage tanks were limited to flowing at a rate of 2.5L/sec. We needed a minimum of 8.5L/ sec of recycled water to fill the water storage tanks and supply enough recycled water to sustainably irrigate the open spaces.

The bores were restricted at the depth they could be drilled due to the area only having a thin fresh-water lens. Drilling further than 9 metres and over-pumping at a higher flow rate would result in drawing brackish water (more saline than freshwater), which isn’t fit for irrigating our green spaces.

What we did

Working with Water Corporation, we expanded our water recycling scheme to deliver a sustainable water supply and further reduce the reliance on our native groundwater extraction.

We produced more than 51,000KL of recycled water in just one year for public open space. This volume of recycled water supports over 5 hectares of public and active space.

These active spaces usually require reticulated water. The City has been proactive in accessing and expanding recycled treated wastewater to accommodate this growing need.

The Halls Head Water Resource Recovery Facility (WRRF) treats wastewater to a tertiary standard using an activated sludge-type plant consisting of 2 oxidation ditches and 4 clarifiers. The recycled water is transferred to onsite infiltration basins following treatment, further improving recycled water quality via aquifer treatment and dilution with groundwater.

The infiltration basins provide aquifer recharge where we reclaim recharged groundwater via abstraction bores. The recycled water is stored in large tanks, ready to irrigate our public spaces. Recycled water from WRRFs is regulated by the Department of Health (DoH) and meets strict criteria for approval. Environmental Risk Assessments are also undertaken to ensure the reuse schemes are sustainable with ongoing recycled water quality analysis.

We increased the water flow rate to the storage tanks by installing solar bores alongside the 2 current production bores. The works also included upgrades to the pipeline from an 80mm mainline water supply to a 160mm mainline water supply. This was done to enable the increase in flow rate.

Solar-powered bores.

The solar energy generated powers the solar bores to fill the storage tanks during the day. The increase in the flow of 10.5L/sec to the tanks ensures the current public spaces connected to the scheme receive the water they need during the drier months. 

Recycled water storage tank.

We've also identified that an additional 3 recreational spaces – Quandong, Lakes and Mogum public open spaces could be irrigated from the recycled water stored in the tanks. Once connected to the water supply, this will further reduce our reliance on drawing on groundwater sources. Any extensions in a recycled water scheme are evaluated by the DoH and receive DoH approval if endorsed.

What we’re doing now

Expanding our water recycling scheme will allow greater volumes of recycled water to irrigate more public spaces.

Educating the public about where we irrigate with recycled water is also important to ensure we comply with DoH regulations and protect public health. This includes:

• Having appropriate signage around the public open spaces where recycled water is used
• Ensuring adequate buffer zones around sensitive amenities such as BBQs and water fountains
• Ensuring we only irrigate DoH-approved recycled water spaces during the evening to allow plenty of drying time before public use occurs.

The recycled water supply DWER licence is currently 145,000kL/year. Currently, only 51,000kL/year is being used, so we have the capacity to increase recycled water use in the future.