Aquifer Storage and Recovery using Wastewater

Synopsis

The City of Mandurah, a Water Campaign™ participant since 2002, recognises the need to take a holistic view of water management and thus sees groundwater as a vital resource to assist their municipality manage appropriately.

In June 2000 the City of Mandurah began working with land developers, Mirvac Fini, the Water Corporation and the CSIRO Land and Water to develop the Halls Head Indirect Reuse project.

The project was developed in response to a growing need for a non-scheme water source suitable for irrigation purposes in the City of Mandurah. The City proposed that a source of treated wastewater be developed to meet the need for irrigation of selected parks and recreational grounds.

The wastewater is infiltrated to the aquifer from the Water Corporation’s Halls Head Wastewater Treatment Plant and then recovered for irrigation as naturally filtered irrigation water.

In 2004 the council endorsed Phase two of the project which will involve expansion of the project to a number of new open spaces constructed by a developer.

Motivation for Investigating Wastewater Aquifer Storage and Recovery

As with most local governments in the Perth metropolitan region the City of Mandurah utilises groundwater to irrigate areas of open space and playing fields.

In Western Australia, the current drying climate and the widespread use of groundwater by commercial and private users has meant that groundwater levels in some areas are falling causing changes in wetland hydrological regimes, acid sulphate soils and saline groundwater intrusion in extreme cases (Government of Western Australia, 1998 & Government of Western Australia, 2004). Reduced availability of groundwater has also meant that the City has found it difficult to find a sustainable supply of water to maintain the condition of its parks and gardens.

It is for these reasons that the City of Mandurah has become involved in investigating the feasibility of wastewater reuse and aquifer storage and recovery.

Savings and Benefits

It is anticipated that once wastewaster is supplied to all proposed reserves approximately 221,000KL of groundwater will be saved annually on the second stage of the project alone.

Process

The Halls Head Indirect Reuse Project uses natural aquifers as an “underground dam”. The aquifer is artificially recharged by pumping treated wastewater into surface infiltration ponds. The ponds then allow the treated water to leach through the sandy soils into the aquifer below. Testing has shown that the quality of the treated wastewater is comparable, and in some cases superior to the water naturally occurring in the aquifer. A significant aspect of the project has been long term water quality monitoring by the CSIRO to assess any possible water quality, health or environmental issues associated with the recovered water. “The results obtained have indicated that the recovered water obtained utilising indirect reuse is of a suitable quality for irrigation purposes and has negligible associated health or environmental risks.” (Toze S, 2004)

The aquifer provides a natural aquatic environment free from evaporation loss. It also reduces the need to construct artificial large-scale water storage facilities such as surface dams.

The project has been carried out in two stages. For the last four years the housing development’s stages 1 to 4 has been irrigated by the wastewater. In 2004 the City of Mandurah endorsed an expansion of the project which will potentially see further stages of the development being irrigated with wastewater, as well as a local reserve, an oval and a local country club.

In October 2004 the City of Mandurah, Mirvac Fini and the CSIRO jointed received the Water Corporation Award for Water Treatment and Recycling through the WA Water Industry Awards for the Halls Head Indirect Reuse Project.

Savings and Benefits

It is anticipated that once wastewaster is supplied to all proposed reserves approximately 221,000KL of groundwater will be saved annually on the second stage of the project alone.

Costs

While the developer will bear the initial costs for developing the scheme infrastructure the City of Mandurah will bear the ongoing maintenance and the increased water costs associated with treated wastewater.

Currently the charges for the treated wastewater are 44.5 cents/KL. Typical costs for water supplied by artesian bore are 26 cents/KL to 30 cents/KL. This equates to an approximate increase in councils watering costs of $36,000 per year.

However the costs compare favourably with the cost of potable water which is approximately $1 a KL (Water Corporation 2004). The use of this wastewater also ensures that the groundwater supplies continue to be viable. If the groundwater supplies are over abstracted and saline water intrudes, the city would need to switch their irrigation to potable water, increasing their water costs significantly in the long term.

References

1. Toze, S. 2004 Extract from Application Submitted for WA Water Industry Awards for Hall Head Indirect Reuse Project, CSIRO Perth WA
2. Government of Western Australia (2004) Western Australian Proposed Framework for Managing Acid Sulfate Soils, Department of Environment.
3. Government of Western Australia (1998) Water Facts 12 Bore Water Use in Perth Gardens, Department of Environment http://portal.environment.wa.gov.au/(accessed 27 June 005)
4. Water Corporation (2004) 2004/2005 Rates and Charges - Metropolitan Commercial http://www.watercorporation.com.au/residential/Accounts_Rates_Metro_Comm.cfm

(accessed 27th June 2005)

ICLEI-A/NZ would like to acknowledge the assistance of Mr Damien Postma from the Peel Harvey Catchment Council and the City of Mandurah in the production of this case study.

For further information about this project contact:

Mr Damien Postma
LG NRM Officer / Water Campaign Officer
Phone: (08) 9550 3777
Email: damien-p@mandurah.wa.gov.au