Oral Presentation NCGRT/IAH Australasian Groundwater Conference 2019

A series of case studies to highlight the use of geophysics for hydrogeological applications (398)

Karen M. Gilgallon 1 , Heather J. Ballantyne 1 , Brendan A. Ray 1 , Gregory Maude 1
  1. Southern Geoscience Consultants Pty Ltd, Belmont, WA, Australia

Geophysics is useful in a range of hydrogeological settings. A series of short case studies will cover geophysical applications in coastal sedimentary aquifers, fractured rock aquifers, paleochannel aquifers and mine dewatering. Case studies of coastal sedimentary aquifers at Exmouth, and North Perth Basin, Western Australia will highlight the successful use of airborne electromagnetics (AEM) and ground electrical resistivity imaging to map the aquifer structure and saline water interface.

Airborne magnetics, radiometrics and electromagnetics have proved successful in mapping fractured rock aquifers in South West, Western Australia. Magnetics is highly effective in mapping significant faults and fractures while airborne radiometrics and electromagnetics have highlighted areas of shallow bedrock and deeper weathering.

Three paleochannel examples highlight the effectiveness and limitations of airborne and ground electromagnetics (EM), gravity and passive seismic methods. AEM is a successful and fast method to cover large areas but in highly saline areas, mapping the base of the channel is often ineffective. Ground EM, gravity and passive seismic techniques can all be effective in detailed mapping of channel structure and thalwegs.

Pit wall dewatering is necessary to prevent wall failure which may impact safety and production in operating mine sites.  A controlled source audio magneto-tellurics (CSAMT) survey was completed at the Gold Quarry mine on the Carlin Trend in 2009 following a pit wall failure. The survey successfully identified several perched clay aquifers and the main water table. It also delineated the location of faults, structures and saturated sediments. Depressed water tables surrounding dewatering bores were also clearly identified in the data. The survey allowed for rapid, effective placement of dewatering bores and reduced the risk of future pit wall collapse.

These case studies highlight how geophysical techniques can be used as cost effective tools for both detailed and broad hydrogeological problems including de-risking bore placement.