Aquifer Storage and Recovery Feasibility Study, Australian Capital Territory, Australia

WR Evans, Sinclair Knight Merz, 214 Northbourne Ave, Braddon ACT 2612

A feasibility study of the ASR potential of the Australian Capital Territory (ACT) was undertaken as part of a larger study of alternative water supplies for urban usage. The ACT is Australia’s Capital and contains a population of about 350,000 people. Studies have been commissioned to replace up to 3000 ML/yr of potable water being used for non-potable end uses. Strategies that are being considered include stormwater harvesting, wastewater reuse and sewer mining.
ASR is being considered in conjunction with stormwater harvesting ponds, with some detailed desktop studies of harvesting costs being undertaken.

The ACT lies in southeastern Australia and experiences a temperate climate; receiving about 620 mm/yr rainfall opposed to about 1650 mm/yr evaporation. Rainfall has been below average since the year 2000 and temperatures have also increased since that date.

The hydrogeology of the ACT is comprised predominantly of fractured Paleozoic rocks with some minor alluvium along the main surface water drainage lines. Bore yields are highly variable, but rarely exceed 10 L/sec; storativity is low (less than 5%). Hydraulic gradients are variable, but steep, with the watertable a subdued reflection of the topography. Most groundwater discharge is as base flow to the areas streams.

Sites of enhanced bore yield have been identified as areas where small ASR schemes may yield between 50 and 200 ML/yr. A number of different ASR scheme designs have been proposed and these have been incorporated into a least cost approach to ranking stormwater harvesting options by CSIRO.

Consideration has been made of the existing regulatory system. The urban area has been sub-divided into several catchments, with each having a sustainable yield estimate. In most cases, the full sustainable yield has been allocated to users. This means that ASR will be operated in a fully allocated system. As well, water quality objectives have been set for each catchment area and these are a primary constraint on the water quality able to be injected.

The paper will discuss the various ASR scheme designs, the match of each scheme to a stormwater harvesting pond and some basic information on costings and ranked schemes.