Groundwater residence time in the Condamine River Alluvial Aquifer (SE-QLD)

Many gigalitres of groundwater have been extracted from the Condamine River Alluvial Aquifer (CRAA) since the 1960s. These groundwater withdrawals have stressed the system and locally altered the groundwater flow paths. Isotopes can provide powerful insights into recharge pathways, flow direction, and the sustainability of groundwater withdrawals from alluvial aquifers. To address some of the regional groundwater concerns we must characterise alluvial groundwater residence time.A total of 31 groundwater samples were collected from privately owned irrigation bores and Qld-DNRM government monitoring bores in the region between Condamine Plains and Dalby. Parameters analysed included: 3H, 14CDIC, 222Rn, 87Sr/86Sr, δ13CDIC, water δ2H and δ18O, sulfate δ34S and δ18O as well major, trace and REE elements.Distance from primary recharge areas (rivers) provides the main control on groundwater residence time in the CRAA. This is supported by the following observations:1) Groundwater between the Condamine River and its northern branch has low TDS (~400 mg/L), is Na-HCO3-type and has detectable 3H, indicating a proportion of modern recharge (