Since the 1970's rainfall in south west WA has reduced by around 19 per cent, streamflow to Perth’s dams has declined even more dramatically. In 2009, in response to the early signs of a drying climate, the WA Water Corporation released a 50-year plan to secure Perth's water supply. In 2011 this was followed by a 10-year plan. As part of the implementation of these plans Water Corporation has progressively added new sources of water that are independent of climate to help secure supplies. These sources include seawater desalination and groundwater replenishment.
Water extracted from groundwater systems is particularly important for meeting the water needs of Perth. Groundwater currently provides about 46% of Perth’s total water supply.
Groundwater replenishment is an approach where wastewater is treated to drinking water standards, and injected into aquifers to recharge them. The injected recycled water is then stored in the aquifers which also provides further natural treatment capacity, and extracted when required through existing production wells. By injecting recycled water it is possible to reduce the reliance on rainfall to replenish the aquifers. In the long term, Water Corporation's 50-year plan indicates that groundwater replenishment could contribute to as much as 20% of Perth's drinking water supply in 2060.
However, before the required approvals could be obtained to inject recycled water into drinking water supply aquifers it was necessary to demonstrate to the Department of Health, Department of Water and Department of Environment and Conservation (now Department of Water and Environmental Regulation) and the broader community that it was safe to do so and that there would be no adverse impacts on water security, human health and the environment. In 2005 CSIRO was commissioned by the WA Water Corporation to carry out a program of research to help build the case for the Managed Aquifer Recharge (MAR) of Perth’s aquifers.
Helping to develop regulatory frameworks and policies for aquifer replenishment
CSIRO developed a series of solute and reactive transport models at different scales that allowed them to characterise the water quality changes and estimate the flow of the injected water through the aquifer. These models enabled researchers to predict the long term behaviour of the water injected into the aquifers. Specifically, when injected water would reach an extraction well and what the quality of that water would be.
The well field conditioning process undertaken proved very successful in maintaining permeability of the injection site. The WA Water Corporation are achieving injection rates of 175 litres per second at each injection well. This is a very high injection rate compared rates achieved at similar aquifer replenishment schemes around the world. Since commencing injection in late 2017 the scheme has operated without any loss of permeability.
CSIRO was instrumental in helping to develop the regulatory frameworks and policies that have allowed aquifer replenishment to occur. Their support has also helped to ensure community acceptance of the recycling of waste water and its injection into the aquifer. That acceptance was demonstrated by the lack of any community opposition to the recent decision to expand the amount of injected water from 14 GL to 28 GL a year.
Improved security and sustainability of water supplies
The West Australian managed aquifer replenishment project has:
- demonstrated that the injection of recycled water did not pose any threat to the health of humans or the environment
- increased community confidence in the aquifer replenishment program and helped WA Water Corporation to maintain its social licence to operate
- enabled the WA Water Corporation to obtain a licence to extract water from Perth’s aquifer equivalent to the amount of recycled water it has injected
- improved the security and sustainability of Perth’s water supplies
- helped WA Water Corporation avoid costs estimated to be $356.5 million in 2017/18 dollars.