Use of Hydrochemistry, Stable Isotope, Radiocarbon, 222Rn and Terrigenic 4He to Study the Geochemical Processes and the Mode of Vertical Leakage to the Gambier Basin Tertiary Confined Sand Aquifer, South Australia

Abstract

Abstract:The mode of vertical recharge to aquifers is important to the application of appropriate recharge estimation methods. This study identifies the origin, geochemical evolution and mode of vertical leakage to the Gambier Basin confined aquifer, south east of South Australia. The recharge zone spans areas of the Glencoe-Nangwarry-Nagwarry (GNN). The Hundreds of Glencoe and Nangwarry are in South Australia, and the Parish of Nagwarry adjoins Nangwarry in western Victoria. The plot of stable isotopes of water molecules, δ 2 H versus δ 18 O, indicates that local rainfall with minor surface evaporation is the source of recharge. The results of hydrochemical analysis indicate that the sources of ions in the recharge zone groundwater are derived from carbonate and silicate weathering with cation exchange. The majority of water types (66% of samples) within the South Australian part of the recharge zone show Ca-Na-HCO 3 -Cl due to carbonate dissolution processes, and about 83% of samples within the Victorian part of the recharge zone show Na-Ca-HCO 3 -Cl water types, indicating cation exchange or mixing with other waters. The influence of faults on vertical leakage was studied at eight sites located in the Nangwarry and Nagwarry area using electrical conductivity logging, measuring the concentration of radiocarbon activity, δ 18 O, 222 Rn and terrigenic 4 He in the vertical profiles. Results show that regardless of land use in the study area, the interconnection of the unconfined Tertiary limestone aquifer with the Tertiary confined sand aquifer occurs, via both diffuse and preferential flows. Thus, the application of conventional vertical leakage estimation methods using Darcy's equation or the application of tracer techniques may be inappropriate unless the duality of the flow system is considered.

Effects of Grass and Forests and the Infiltration Amount on Preferential Flow in Karst Regions of China

“…The rapid process of preferential flow reduces the water retention time [18]; in order to make a profound study about the law of water cycle and the practical significance of natural forest and artificial forest on bottom of slope, the geochemical processes and the mode of vertical leakage need to be investigated [19]. At present, most studies that focus on different water inputs have lots of effects on preferential flow under different soil architectures [1], land cover [20], and land use [21].…”

The Control of Groundwater Flow Systems and Geochemical Processes on Groundwater Chemistry: A Case Study in Wushenzhao Basin, NW China

“…In contrast, type 2, 3, 4 and 5 waters exhibit a significant deviation from the 1:1 relation line and plot above it, indicating the simple dissolution of carbonate and gypsum alone could not interpret their chemical compositions. This may be caused by the cation exchange, silicates weathering or evaporites dissolution [47]. Figure 9c shows that majority of these waters plot above or below the theoretical line of weathering of plagioclase (y = x), suggesting silicate weathering is not the major source of Na + .…”

Groundwater Chemistry Regulated by Hydrochemical Processes and Geological Structures: A Case Study in Tongchuan, China

“…Stable isotopes are commonly used in order to study the origin and chemical evolution of groundwater [31][32][33]. The deuterium excess (d -excess = δD -8 × δ 18 O) is usually used to describe the evaporation influence on water bodies compared to that of precipitation [31].…”