Influence of water level fluctuation on groundwater solute content in a tropical south Indian region: a geochemical modelling approach

Abstract

Groundwater levels in the Dharapuram region exhibited drastic seasonal changes. Hydrogeochemical analysis were performed on the groundwater samples collected during January (post-monsoon) and July (pre-monsoon) in 2009 to understand the chemical changes and related process encountered during the fluctuated water table. Dominant water type in the study area was Na–Cl with smaller contributions from Ca–Cl and mixed Ca–Mg-Cl type of water. Gibbs plot employed to differentiate the controlling mechanisms of hydrochemistry, which showed that rock-water interaction is the dominant process. However, bivariate plots identified silicate weathering is the major contributor to the rock weathering. Higher concentration of Cl in the groundwater is suggesting the anthropogenic sources to ionic chemistry. Precise examination of the hydrochemical changes with rise and fall in the water table showed three distinct behavior; the EC, increased with increasing water level (type 1), increased with decreasing water level (type 2) and no significant changes with WL fluctuation(type 3). Aqueous speciation modeling was carried out on representative samples. This shows that dissolution and deposition of the carbonate minerals, mixing of textile wastes and the irrigation return flow were the major processes prevailing in the study area. However, the changes in chemical kinetics encountered during seasonal water level fluctuation are also controlling the hydrogeochemistry of this hard rock terrain.