Indian Journal of Science and Technology

Abstract

Objective: In present study, hydrochemical data were used to characterize the hydrogeochemical processes and to identify groundwater flow systems in Bengal Delta aquifers, Bangladesh. Methods: Regarding this, 202 shallow, 26 intermediate and 100 deep groundwater samples were collected from the study area for major ion analyses. It is observed that the shallow and intermediate groundwater samples are dominantly Ca-Mg-HCO3 type, and the deep groundwater is mainly of Na‒Cl‒HCO3 and Na‒Cl types. In deep groundwater, the loss of Ca2+ are ion exchanged for Na+ along the flow paths, which are initially enriched in Ca2+. The Na-HCO3 type deep groundwater appear in the coastal confined aquifers, whereas Na-Cl type groundwater are found in wells depth ranging from 200-250m. With some local exceptions, electrical conductivity (EC), pH and Cl- concentrations for both shallow and deep groundwater gradually increase generally from north-south direction in the study site. Findings: The observed results clearly indicate the presence of three groundwater systems: (i) the shallow groundwater characterized by low ionic concentration; (ii) intermediate groundwater with less evolved ionic chemistry; and (iii) the deep groundwater with higher ionic concentration. Application: This study enables to conceptualize three groundwater flow systems: namely shallow fast circulating fresh young water mixed and moderately mineralized groundwater representing a transition system between the overlying shallow and underlying deep aquifers and the highly mineralized deep groundwater.

Keywords: Bangladesh, Bengal Delta, Groundwater flow, Hydrogeochemistry