Carbon-14 (14 C) has been measured in groundwater for over half a century and remains a widely used tool for understanding groundwater flow systems. Ultimately, the usefulness of 14 C as a groundwater tracer relies on the ability to distinguish between changes in concentration due to various chemical/physical processes (e.g. chemical reactions with solid carbonate material, conditions at the water table), and changes due to ageing along flow paths, the latter being most informative of groundwater flow conditions. To this end, a number of correction methodologies have been developed to account for chemical modifications in groundwater systems. In this paper, we implement two different single sample correction models, one for closed and one for open system carbonate dissolution in conjunction with a Markov chain Monte Carlo (MCMC) approach at two sites; the sedimentary Port Willunga Formation Aquifer in South Australia and a fractured rock aquifer in the Hamersley Basin, northwest Australia. For comparison, we include argon-39 (39 Ar) data taken from some of the wells sampled and use a mixing envelope constraint in the MCMC procedure. We found that considering all of the errors associated with 14 C correction resulted in a distribution of values to consider for groundwater dating procedures. When accounting for all parameters associated with single sample correction techniques, the associated error was 10 times greater than the analytical errors. Additionally, inclusion of the 39 Ar data produced mixed results, with little improvement observed in the Port Willunga Aquifer (closed system correction), and a significant improvement observed at the Hamersley site (open system). This is most likely due to the mixing caused by long screens and the sensitivity of the open system correction model. Our results highlight the importance of considering all sources of error in groundwater dating studies.

A lack of closely spaced datasets on layer elevations, aquifer parameters, identification of areas with high recharge potential, dominant conduit porosity zones, and well defined boundary conditions hampers the ability of groundwater models to produce a reliable water balance. Typically, geological structure, aquifer properties, and groundwater heads are obtained from point measurements which are sparse. The drillhole information in aquifers is usually available at locations far apart, distances ranging from hundreds to thousands of meters. Furthermore, pump tests are usually conducted at limited locations and generalized to the aquifer. This limited knowledge leads to errors in the conceptual understanding of the aquifer. In this study, Airborne Electromagnetic Survey (AEM) was used to define base elevations of the aquifers where drillhole information was lacking. Surface Nuclear Magnetic Resonance (sNMR), borehole NMR, Transient Electromagnetic (TEM), and downhole geophysical surveys have given new insight to the conceptualization of hydrogeological framework. These methods are relatively low in cost compared to traditional well drilling and provide information on layer elevations, aquifer parameters, point and diffuse recharge zones, and conduit porosity zones in the profile, which improves our definition of the boundary conditions. From a practical point of view, combining drillhole information with a variety of geophysical techniques provides sound datasets to develop a comprehensive conceptual model. This in turn can be used to build a robust groundwater model.