The application of airborne geophysical data as a means of better understanding the efficacy of disposal basins along the Murray River: An example from Stockyard Plains, South Australia

Abstract

The pumping and disposal of saline groundwater from the margins of the River Murray in South Australia is an integral part of the State Government?s salinity management strategy. It is specifically aimed at reducing ground water levels and salt accession to the River Murray. Large volumes of saline water are typically disposed at the land surface in what are referred to as ``saline-disposal basins'. Although these disposal basins are now common, surprisingly little is known about their long-term efficacy or environmental effects. This study focuses on the analysis and interpretation of RESOLVE frequency domain helicopter electromagnetic data acquired over the Stockyard Plains saline-water disposal basins located southwest of Waikerie, South Australia, with a view to determining the extent of saline plume migration and informing our current understanding of the hydrodynamics of saline groundwater disposal in the area. The airborne EM data was calibrated using conductivity borehole data and statistical methods prior to modelling. Two sets of conductivity models were generated using smooth layered inversion and constrained layered earth inversion. The constrained inversion model provided information on the depth, thickness and presence or absence of aquitards, specifically the Blanchetown Clay, and map variations in groundwater conductivity in the region around the existing natural disposal basins. The smoothed inversion model defined the extent and condition of the groundwater mound beneath the existing disposal basin. In addition these data can be used to investigate the potential for extending disposal options in the vicinity of the existing basin by identifying areas where aquitards (the Blanchetown Clay) are present or absent.