Oral Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Groundwater recharge at the eastern intake beds of the Great Artesian Basin using multi-isotope studies (379)

Axel Suckow 1 , Alec Deslandes 1 , Christoph Gerber 1 , Andrew Taylor 1 , Matthias Raiber 2 , Damian Barrett 3 , Karina Meredith 4
  1. Land and Water, CSIRO, Urrbrae, SA, Australia
  2. Land and Water, CSIRO, Dutton Park, QLD, Australia
  3. Energy, CSIRO, Acton, ACT, Australia
  4. ANSTO, Lucas Heights, NSW, Australia

Objectives

Large sedimentary basins with multiple aquifer systems, such as the Great Artesian Basin (GAB) in Australia, are difficult to study because of the very large time scales associated with groundwater flow. The GAB is the world’s largest and deepest artesian groundwater basin and has become increasingly stressed due to demand from multiple competing industries (agriculture, oil, coal and gas). Quantifying groundwater recharge is crucial for understanding the water balance for this economically and culturally important multi-aquifer system. The complexity of the GAB can only be dealt with by applying multiple lines of evidence including environmental isotopes, supported by hydrochemical, sedimentological, and geophysical observations.

Design and Methodology

Three studies on the recharge areas of the GAB investigated recharge to the Hutton Sandstone and the Precipice Sandstone (QLD) and the Pilliga Sandstone (NSW). Multiple environmental tracers (major ion chemistry, 18O, 2H, 3H, 13C, 14C, 36Cl, 87Sr/86Sr, 85Kr, 81Kr, noble gases) were measured. Recharge rates were derived from tracer concentration profiles and aquifer cross-sections with porosity derived from previous studies.

Conclusions

Tracer results in the Precipice Sandstone are consistent with pumping test data and re-injection of coal seam gas produced water, suggesting high hydraulic conductivities. They provided the first estimate of average long-term annual recharge to this deep confined aquifer, which is of a similar order of magnitude as today’s industrial re-injection of CSG water.

A consistent interpretation of tracers within the Hutton Sandstone was only possible assuming dual porosity involving diffusive tracer exchange between flowing and stagnant pore spaces. The new results highlight that the Hutton Sandstone receives only ~ 3% of the recharge previously estimated using Chloride Mass Balance (CMB) at the intake beds.

Results for the Pilliga Sandstone provide evidence for two distinct flow paths, with the southern path providing a much higher flow velocity than the northern path. 85Kr and 81Kr measurements also validated the initial findings derived from using 14C and 36Cl, but are much more robust.