Detecting inter-aquifer leakage in areas with limited data using hydraulics and multiple environmental tracers, including 4He, 36Cl/Cl, 14C and 87Sr/86Sr

Abstract

The investigation of regionally extensive groundwater systems in remote areas is hindered by a shortage of data due to a sparse observation network, which limits our understanding of the hydrogeological processes in arid regions. The study used a multidisciplinary approach to determine hydraulic connectivity between the Great Artesian Basin (GAB) and the underlying Arckaringa Basin in the desert region of Central Australia. In order to manage the impacts of groundwater abstraction from the Arckaringa Basin, it is vital to understand its connectivity with the GAB (upper aquifer), as the latter supports local pastoral stations and groundwaterdependent springs with unique endemic flora and fauna. The study is based on the collation of available geological information, a detailed analysis of hydraulic data, and data on environmental tracers. Enhanced inter-aquifer leakage in the centre of the study area was identified, as well as recharge to the GAB from ephemeral rivers and waterholes. Throughout the rest of the study area, inter-aquifer leakage is likely controlled by diffuse inter-aquifer leakage, but the coarse spatial resolution means that the presence of additional enhanced inter-aquifer leakage sites cannot be excluded. This study makes the case that a multi-tracer approach along with groundwater hydraulics and geology provides a tool-set to investigate enhanced inter-aquifer leakage even in a groundwater basin with a paucity of data. A particular problem encountered in this study was the ambiguous interpretation of different age tracers, which is attributed to diffusive transport across flow paths caused by low recharge rates.

Palaeohydrogeology and Transport Parameters Derived from 4He and Cl Profiles in Aquitard Pore Waters in a Large Multilayer Aquifer System, Central Australia

“…In this study, we examine vertical groundwater flow and solute transport through an aquitard separating the GAB and the underlying Arckaringa Basin. The aquitard of interest is situated between two aquifers with long residence times of water, due to the low recharge rates in the arid climate [49]. Chloride, 4 He, and stable isotopes of water in conjunction with numerical and analytical modelling were used to quantify flow velocities and establish the connectivity between the two basins at the site studied.…”

Geochemical and Isotopic Assessment of Regional Groundwater Flow and Aquifer Connectivity in the Lisbon Valley, Utah

“…These properties of Sr and Rb thus make them ideal tracers in many groundwater systems. As 87 Rb decays and the concentration of 87 Sr increases, the increasing concentration of 87 Sr can be compared to the amount of non-radiogenic 86 Sr -the ratio of which can provide insight into water-rock reactions (Campbell et al, 2008;Priestly et al 2017), trace groundwater movement (Campbell et al, 2008;Priestly et al 2017), and identify sources of salinity (Brenot et al, 2014).…”

“…Major ion chemistry, trace metals, solute isotopes, and age tracers can be indicative of whether mixing is occurring between two aquifers, because if mixing were occurring, one would expect the values of these geochemical parameters of each water to be similar and/or follow a mixing trend (Campbell et al, 2008;Johnson et al, 2015;Priestly et al, 2017;Li et al, 2018). The unique geochemical and isotopic signatures of each aquifer at LVMC, and lack of mixing trends between aquifer endmember compositions, suggests that limited cross-formational flow is occurring between the BCA and the NA.…”

“…Aquifer connectivity and the potential for cross-formational flow is an issue pertinent to many fields including oil and gas production (e.g., Campbell et al, 2008), mining (e.g., Li et al, 2018), and water resources development and protection (e.g., Johnson et., al 2015;Priestly et al, 2017). For example, understanding regional groundwater flow and assessing aquifer connectivity can aid in the determination of where harmful byproducts of any of the aforementioned activities may end up and how to better protect freshwater resources based on this knowledge.…”

“…hydrogeologists take a subsurface-based approach, relying on data collected from arrays of boreholes, but often not directly observing fault characteristics (Bense et al, 2013). By using a suite of geochemical tracers combined with physical hydrogeological conceptions, it may be possible to delineate if cross-formational mixing is occurring and to what extent (Campbell et al, 2008;Johnson et al, 2015;Priestly et al, 2017;Li et al, 2018).…”