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

Abstract

A study of chloride and 4He profiles through an aquitard that separates the Great Artesian Basin from the underlying Arckaringa Basin in central Australia is presented. The aquitard separates two aquifers with long water residence times, due to low recharge rates in the arid climate. One-dimensional solute transport models were used to determine the advective flux of groundwater across the aquitard as well as establish any major changes in past hydrological conditions recorded by variations of the pore water composition. This in situ study showed that both diffusion and slow downward advection (vz=0.7 mm/yr) control solute transport. Numerical simulations show that an increase in chloride concentration in the upper part of the profile is due to a reduction in recharge in the upper aquifer for at least 3000 years. Groundwater extraction since 2008 has likely increased chloride and 4He concentrations in the lower aquifer by pulling up water from deeper layers; however, there has been insufficient time for upward solute transport into the pore water profile by diffusion against downward advection. The transport model of 4He and chloride provides insight into how the two aquifers interact through the aquitard and how climate change is being recorded in the aquitard profile.

Groundwater Salinization and Flushing During Glacial‐Interglacial Cycles: Insights From Aquitard Porewater Tracer Profiles in the North China Plain

“…Samples were analyzed for Cl concentration using ion chromatography (IC) at Flinders University, Adelaide, with a precision of ≤2.5%. The measured chloride concentrations obtained with the 1:5 dilution method were converted into an in situ Cl concentration of porewater, as per Priestley et al (2017).…”

“…Batlle‐Aguilar et al (2016) present a summary of porewater velocities in aquitards derived using chemical methods from around the world and show that porewater velocity generally ranges between 0.01 and 1 mm/yr. Most studies assume a constant advective velocity caused by hydraulic head differences in the aquifers above and below the aquitard (Harrington et al, 2013; Priestley et al, 2017) or driven by sediment compaction (Sanford et al, 2013). In some cases, particularly for salt water intrusion caused by transgression, diffusion may solely be adequate to reproduce tracer profiles (Kuang et al, 2016).…”

“…The impact of changing hydraulic gradient—for example, reversal in direction due to intensive groundwater extraction above or below the aquitard—may also be important in controlling solute profiles. This is generally poorly understood and warrants further exploration (Priestley et al, 2017), particularly in systems where the length of time and intensity of groundwater extraction are significant, as in the NCP.…”

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

“…In the article titled "Palaeohydrogeology and Transport Parameters Derived from 4 He and Cl Profiles in Aquitard Pore Waters in a Large Multilayer Aquifer System, Central Australia" [1], Mr. Stanley D. Smith was missing from the authors' list. Mr. Stanley made a significant contribution in helping with the core sampling protocol, canister leak testing, and discussing modelling methods.…”