Backing up the AEM – unravelling a palaeovalley fill for groundwater exploration in the APY Lands

SummaryA major constraint on development in the Anangu Pitjantjatjara Yankunytjatjara (APY) Lands is the lack of reliable water supplies. Sandstone strata found within palaeovalleys has long been recognised as potentially productive aquifers in outback South Australia. Although the APY Lands are known to contain such geologic features, their development as a viable water supply has been hindered by an acute lack of knowledge.An extensive airborne electromagnetic (AEM) survey was acquired as part of the Goyder Institute for Water Research’s Facilitating Long-term Outback Water Solutions Stage 3 (G-FLOWS S3) project in order to improve the understanding of groundwater resource potential in this remote region of South Australia. The AEM data revealed an intricate drainage pattern below the modern-day land surface that represents palaeovalleys. This facilitated the spatial refinement of these palaeodrainage features and provided a better understanding of their overall thickness.A targeted drilling campaign followed the AEM survey. Whereas the AEM data covers a large area of the APY Lands, drilling focused on two areas near the community of Kaltjiti (Fregon) in the eastern part of the APY Lands. Two hydrogeological test sites helped to understand and monitor the groundwater system associated with the Lindsay East Palaeovalley. Furthermore, drilling determined the true depth of the palaeovalley and provided a stratigraphic record. This enabled the validation of the AEM hydrogeophysical model, which included the identification of groundwater bearing zones within the palaeovalley. In total, 11 groundwater wells were constructed and continuous drill core was collected at the two sites.Drilling near the centre of the Lindsay East Palaeovalley suggests there are at least three groundwater-bearing zones. The basal coarse-grained sandstone unit of the younger palaeovalley fill shows promise as a productive aquifer, with development yields varying between 5 and 20 L/sec and salinities of <1000 mg/L TDS.