Hydrochemical characterization and quality appraisal of groundwater from Pungar sub basin, Tamilnadu, India

The Pungar sub basin is located in the central part of South India. The geology is mainly composed of Archean crystalline metamorphic complexes. Increased population and intensive agricultural activity make it imperative to assess the quality of the groundwater system to ensure long-term sustainability of the resources. A total of 87 groundwater samples were collected from bore wells for two different seasons, viz., Pre monsoon and Post monsoon and analyzed for major cations and anions. Semi-arid climate, high evaporation rate and nutrient enrichment are the key features for EC enrichment. Higher NO3^- and Cl^- were observed in groundwater samples. The sources of Ca^2+, Mg^2+, Na^+ and K^+ are from silicate weathering process. The facies demarcation suggests base exchanged hardened water. Gibbs plot suggests chemical weathering of rock forming minerals along with evaporation. The plot of (Ca^2+ + Mg^2+) versus (SO^2- 4 + HCO^- 3 ) suggests both ion exchange and reverse exchange processes. The plot of (Na^+ + K^+) versus TZ^+ shows higher cations via silicate weathering, alkaline/saline soils and residence time. The disequilibrium index for carbonate minerals point out influence of evaporation and silicate minerals favor incongruent dissolution. Mineral stability diagrams signify groundwater equilibrium with Kaolinite, Muscovite and Chlorite minerals. Comparison of groundwater quality with drinking standards and irrigation suitability standards proves that majority of water samples are suitable for drinking purpose. In general, water chemistry is guided by complex weathering process, ion exchange and influence of agricultural and sewage impact.