GSV Report 66 - Preliminary assessment of the groundwater resources in the Port Phillip region

Category: Geological Survey Reports	Product Code: MP-R-37666
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Abstract The Port Phillip Region is defined as the whole of Port Phillip Bay and the 9,790 km² land area draining into it. The bay is surrounded by land of low relief, rising to over 1200 m AHD in the northeastern part of the Region. All streams drain to the bay; the largest, the Yarra River, drains 52 percent of the catchment. The climate of the region is temperate; air temperature ranges from near 0° to about 36°C and rainfall from an annual mean of 400 mm in the west to 1600 mm in the east. More than two-thirds of Victoria's population and a higher proportion of its industrial development are within the study area. About 60 precent of the land is utilized for agricultural purposes, 12 percent is built-up residential and less than 1 percent is developed for industrial purposes. Residential and industrial development is mainly in or near the periphery of the built-up areas of Melbourne and Geelong.

The geological sequence comprises two main divisions: a relatively impervious basement of folded Palaeozoic and Mesozoic sediments and igneous intrusives, and an overlying cover of Cainozoic sediments and igneous extrusives of variable distribution, thickness and permeability. The Cainozoic cover consists of the Werribee Formation, Older Volcanics, Fyansford Formation, Brighton Group, Newer Volcanics and Quaternary deposits including the Wannaeue and Bridgewater formations (dune limestones) of the Nepean Peninsula.

The basement rocks generally constitute a poor groundwater resource, wheras the Cainozoic rocks contain valuable aquifers; the main aquifers occur in the sand, gravel and/or limestone of the Werribee Formation, Fyansford Formation-Brighton Group aquifer system and the Wannaeue and Bridgewater formations. There are important aquifers also in the basalts of both the Older and Newer Volcanic series. With the exception of the Fyansford Formation-Brighton Group aquifer system in the Oakleigh-Dingley-Black Rock area, the Older Volcanics in the Silvan-Wandin area, the Wannaeue and Bridgewater formations and the Silurian basement rocks in the Kinglake area, the waters in the aquifers in the Port Phillip Region are only of marginal to poor quality. These waters are mainly suitable only for stock watering and industrial uses, but they have potential for domestic use if mixed with high quality mains water of if suitably treated to improve their quality. Groundwater discharge from these aquifers is either onshore into surface streams or offshore directly into the bay; annual offshore discharge from all aquifers in the region is of the order of magnitude of 5 x 10⁷ m³.

Pollution of groundwater mostly arises from waste disposal practices and is most critical in the Newer Volcanic aquifers in the industrial areas of the western suburbs of Melbourne. Contamination of groundwater resulting from the disposal of wastes into disused sand pits in the southeastern suburbs of Melbourne is serious only on a local level. Regionally the arenaceous aquifer material in this area is capable of attenuating much of the pollutants from the groundwater. Areas of potential groundwater pollution include the industrial areas of Geelong and the numerous unsewered holiday resorts around the bay.

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Bibliographic reference Leonard, J.G., 1981. Preliminary assessment of the groundwater resources in the Port Phillip region. Geological Survey of Victoria Report 66. Department of Minerals & Energy, Victoria.