Determining the preliminary assessment extent

The development of the PAE for the Arckaringa subregion was carried out by South Australian Department of Environment, Water and Natural Resources and only a summary of their work is provided in this section.

The following methodology was used to formulate the Arckaringa PAE:

  • The geological Arckaringa Basin boundary and the mapped areas of economic coal beds and lodged exploration licences (obtained from SA Department of State Development (DSD)) were used as the starting point for calculations.
  • Coal beds outside of Arckaringa Basin were excluded from consideration.
  • Potential for mining related water diversions were excluded from the assessment.
  • A potentiometric surface was generated for the Great Artesian Basin (GAB) aquifer (Cadna-owie Formation – Algebuckina Sandstone and equivalents) for the SA and NT portions of the GAB.
  • The extent of potential groundwater drawdown was assumed to be 210 km around coal beds, based upon DEWNR conceptual modelling undertaken previously for the Pedirka Basin. Modelling of the Arckaringa Basin had not been completed at the time of the determination of the Arckaringa PAE.
  • The 210 km drawdown extent was applied in a northerly and easterly direction from coal beds within the basin.
  • Inferred 210 km groundwater drawdown extent assumes potential for up to a 50-year life of mine (LOM) and large scale mining operations.
  • Western and southern boundaries follow the GAB and Arckaringa Basin boundaries taking the further boundary from coal beds to identify potential groundwater connectivity (i.e. Arckaringa Basin formations were excluded from the PAE where outside of the GAB). The extent of the PAE along the south-western boundary of the Arckaringa Basin is based upon extent of potential drawn down from coal beds for which there is limited groundwater knowledge.
  • A 20 km buffer boundary was included as a contingency around known surface waters and groundwater drawdown extents.
  • A 10 km buffer was included where the PAE intersects with fractured rock aquifer (FRA) extents.
  • Paleogene and Neogene sediments were excluded from consideration as a buffer to the GAB where they intersect with coal deposits, as direct impact to these Cenozoic sediments was assumed should open-cut mining occur.
  • GAB discharge springs near the 210 km radius of coal beds in an easterly direction based upon knowledge of DEWNR groundwater system were included.
  • GAB springs of the Lake Eyre supergroup were included with a 5 km buffer around the point location to accommodate the extensive wetland and terrestrial ecosystems that the springs support.
  • The entire Kati Thanda – Lake Eyre (north and south) boundary was incorporated (based on SA Waterbodies mapping).
  • Phreatic surface information was utilised to identify connectivity to shallow groundwater potentially utilised by vegetation (defined as groundwater up to 10 m deep), based upon decisions made by the BA team for other PAEs.
  • Upstream watercourses were excluded where no direct link from mining, where outside the extent of drawdown.

The Arckaringa PAE is a composite of these groundwater and surface water components (Figure 3).

The following data gaps were identified during definition of the Arckaringa PAE:

  • A sufficiently parameterised and tested groundwater model was not available for the entire Arckaringa Basin at the time of definition of the PAE.
  • More information is required to define relationships between alluvial groundwater and the GAB, particularly at the far extent of the drawdown zone of influence.
  • Further refinement is required where overlaps with Stuart Shelf occur, noting that BHP Billiton modelling undertaken as part of the proposed Olympic Dam Expansion Project identified a large cone of depression and impact of groundwater flow to Stuart Shelf.

Figure 3

Figure 3 Surface and groundwater preliminary assessment extents (PAE) for the Arckaringa subregion

Last updated:
5 January 2018