By HARRY CLARKE
THERE’LL be an unusual sight in the skies over parts of the western Darling Downs throughout May as the Office of Groundwater Assessment Impact (OGIA) carries out airborne electromagnetic surveys of the Condamine Alluvium aquifer.
For up to 10 days days beginning on May 8, a helicopter suspending a large hexagonal frame will be flying at low altitude over areas around Dalby and Cecil Plains, gathering data on how coal seam gas development may be impacting groundwater in the region.
A helicopter will fly about 90 metres above the ground with a frame suspended about 35 metres above the ground.
It will take repeated passes with flightpaths between 500m and 1km apart. As it flies overhead it will be sending an electromagnetic signal to the ground and recording the return signal.
The strength of the signal is less than those created by everyday household appliances, the Department of Regional Development, Manufacturing and Water (DRDMW) said.
The Condamine Alluvium is a critical groundwater resource which is part of the Murray Darling Basin System.
It is used by graziers and crop farmers across the region and also encompasses a major coal seam gas field currently being developed by Arrow Energy.
“Much of the Condamine Alluvium lies above the Walloon Coal Measures, which are targeted for coal seam gas extraction along the western margins of the Condamine Alluvium,” a fact sheet published by (DRDMW) says.
“This survey work will help us understand how the depressurisation of coal seams caused by coal seam gas extraction could affect groundwater in the
The OGIA is an independent body responsible for assessing and managing the impacts of groundwater extraction in areas of intensive coal seam gas and coal mining development. It has commissioned SkyTEM Australia to carry out the surveys.
OGIA Director Groundwater Conceptualisation Steve Flook said the survey was an important part of a research project to provide information on the shallow geology and groundwater system in order to better understand potential impacts of resource extraction in the region.
“The survey will also help us improve our knowledge about the potential groundwater connectivity of the Horrane Fault, which is a subsurface geological structure, with the Condamine Alluvium,” Flook said.
“Since 2012, OGIA has significantly advanced the understanding of the groundwater connectivity in the Condamine Alluvium with progressive improvements made over time.
“As part of this process, the Horrane Fault – a geological feature that offsets the coal seams and the deeper formation underneath the Condamine Alluvium – has so far been mapped using seismic and other data.
“While seismic survey has provided a good understanding of the extent of the fault in deeper formations, it has not been effective in shallower parts of the Condamine Alluvium. This is where an airborne electromagnetic survey can support further understanding.”