Radiocarbon dating and the 36Cl/Cl evolution of three Great Artesian Basin wells at Dalhousie,South Australia

The use of ¹⁴C (half-life?=?5,730 years) in modeling the evolution of the ³⁶Cl/Cl ratios in groundwater is reported for the first time. The complexity of the Cl–³⁶Cl system due to the occurrence of different Cl and ³⁶Cl sources and the difficulty of the determination of the initial groundwater ³⁶Cl/Cl ratios have raised concerns about the reliability of using ³⁶Cl (half-life?=?301 thousand years, a) as a groundwater-dating tool. This work uses groundwater ¹⁴C age as a calibrating parameter of the Cl–³⁶Cl/Cl decay-mixing models of three wells from the southwestern Great Artesian Basin (GAB), Australia. It aims to allow for the different sources of Cl and ³⁶Cl in the southwestern GAB aquifer. The results show that the initial Cl concentrations range from 245 to 320 mg/l and stable Cl is added to groundwater along flowpaths at rates ranging from 1.4 to 3.5 mg/l/ka. The ³⁶Cl content of the groundwater is assumed to be completely of atmospheric origin. The samples have different Cl–³⁶Cl/Cl mixing-decay models reflecting recharge under different conditions as well as the heterogeneity of the aquifer.