Hydrogeochemical study of shallow carbonate aquifers, Rameswaram Island, India.

Groundwater quality assessment has been carried out based on physicochemical parameters (pH, EC, TDS, CO(3), HCO(3), Cl, SO(4), PO(4), NO(2), Ca(+2), Mg(+2), Na(+) and K(+)) and metal concentration in the Rameswaram Island from 25 bore wells. The Langelier Saturation Index of the groundwater shows positive values (63% samples) with a tendency to deposit the CaCO(3) in the majority of water samples. Scatter plot (Ca + Mg/HCO(3)) suggests carbonate weathering process, which is the main contributor of Ca(2+), Mg(2+) and HCO(3) ions to the water. Gibbs diagram suggests rock-water interaction dominance and evaporation dominance which are responsible for the change in the quality of water in the study area. NaCl and mixed CaNaHCO(3) facies are two main hydrogeochemical facies of groundwater. Mathematical calculations and graphical plots of geochemical data reveal that the groundwater of Rameswaram Island is influenced by natural weathering of rocks, anthropogenic activities and seawater intrusion due to over exploitation. Weathering and dissolution of carbonate and gypsum minerals also control the concentration of major ions (Ca(+2), Mg(+2), Na(+) and K(+)) in the groundwater. The nutrient concentration of groundwater is controlled to a large extent by the fertilizers used in agricultural lands and aquaforms. Comparison of geochemical data shows that majority of the groundwater samples are suitable for drinking water and irrigation purposes.