Use of geochemical modeling to evaluate the hydraulic connection of aquifers: a case study from Chianan Plain, Taiwan

Abstract

Aquifers are generally composed of highly permeable layers that can conduct a considerable amount of groundwater. Traditionally, aquifer units are correlated through the concept of lithostratigraphy. For low-permeable aquifers, it is difficult to define the spatial distribution of hydrogeological units, and this study attempts to use geochemical modeling to identify the groundwater flow paths in an area of Taiwan. Multiple geochemical analyses, including groundwater chemistry; stable isotopic compositions of hydrogen, oxygen and carbon; and radiocarbon contents were performed. Using these parameters as the constraints of geochemical models, the hydraulic connection was examined between pairs of possibly interlinked wells along four selected cross sections, and the conceptual groundwater model was accordingly established. The resultant model suggests that the hydraulic connection between aquifers should be correlated with the concept of chronological stratigraphy, especially for low-permeable, unconsolidated aquifers. Using Darcy's law, the hydraulic conductivities of the fine-sand aquifers were estimated to be between 3.14x10(-5) and 1.80x(-4) m/s, which are roughly one order of magnitude higher than those derived by in situ pumping tests. The substantial extraction of groundwater over a long period in the studied area could accelerate groundwater flow, leading to an overestimation of the aquifer permeability

Surface soil temperatures of various land cover types within the Chianan Plain, southern Taiwan

“…The Chianan coastal plain is underlain by unconsolidated fine-grained interlayers of fluvial-deltaic deposits from the Pleistocene to a recent age (Lu et al 2008). A hydrogeological cross-section indicated three aquifers from the surface to a depth of 200 m (Fig.…”

“…The Chianan Plain has an area of approximately 75 × 25 km 2 . Monitoring wells within the plain are constructed of stainless steel or polyvinyl chloride, are 10 to 15 cm in diameter, and have depths of 100 to 300 m. Screens of 6 to 24 m in length were installed within the bottom portion of wells and are protected by a surface cement slab of 1 to 2 m in width (Lu et al 2008).…”

Inactive supply wells as conduits for flow and contaminant migration: conditions of occurrence and suggestions for management

“…Viers et al (2012) and Mejia et al (2012) evaluated the potential for nitrate migration from shallow groundwater to deeper strata over broad geographic areas using algebraic and numerical modeling methods, respecitvely. The potential effects of intraborehole flow and transport on a regional scale have also been considered in Poland (Dragon et al 2009), Spain (Jiménez-Martínez et al 2011) and Taiwan (Lu et al 2008).…”

The Role of Leaky Boreholes in the Contamination of a Regional Confined Aquifer. A Case Study: The Campo de Cartagena Region, Spain

“…The Cl/Br ratio, used as an indicator of seawater intrusion or evaporite dissolution, was calculated in all available water samples in order to assess the importance of a third member for mixing calculations (Custodio and Herrera 2000). Finally, 15 environmental isotope analyses (δ 18 O and δ 2 H) were used to confirm the existing connection between aquifers (Lu et al 2008). Isotope analyses were carried out at the AGH Faculty of Physics and Applied Computer Science (Krakow, Poland).…”