Assessment of groundwater quality for drinking and agricultural purposes of a few selected areas in Tamil Nadu South India: a GIS-based study

Hydro-geochemical evaluation is becoming very significant to determine the process involved in the chemical evolution of groundwater. Supply of contaminated drinking water in rural communities is a continuing health issue, leading many resource users to unknowingly consume water with elevated levels of harmful chemicals. The process of pollution risk assessment requires the integration of data that are spatially changeable in nature, making geographic information system (GIS) a perfect tool for such assessments. In this study, GIS was applied to evaluate groundwater quality in Nilakottai block which is one of the endemic fluorosis blocks of Tamil Nadu, South India. The obtained maps may assist water quality personnel in managing and controlling pollution of the study area. The suitability of groundwater quality for drinking and agricultural purposes in the selected area was assessed by measuring physicochemical parameters. For this purpose, 55 water samples were collected from different places of the study area. F⁻ ion leaching depends on groundwater chemistry, including pH and concentrations of HCO₃ ⁻, Na⁺, and Ca²⁺. HCO₃ ⁻ and F⁻ were found to have good positive correlation (r = 0.400). Hydro-geochemical classification of ground water samples throws more light on the possible link between the presences of various ions and their contribution to groundwater chemistry. The GIS maps clearly show the presence of Na–Cl, mixed Ca–Mg–Cl and Ca–Cl as the predominant species in specific regions having a direct bearing on water quality. The relative concentrations of the ions occur in the order Na⁺ > Mg²⁺ > Ca²⁺ and Cl⁻ > HCO₃ ⁻ > SO₄ ²⁻. Water quality index (WQI) was calculated to determine the suitability of water for drinking purpose. The WQI values revealed that all groundwater samples were above 100, which is the permissible limit and, therefore, waters above this level cannot be used for human consumption. Calculated values of Percent Na (%Na), Sodium adsorption ratio (SAR) and Magnesium hazard (MH) indicate that most of the groundwater samples are not suitable even for irrigation of most crops. Rainwater harvesting techniques should be promoted in this study area. Supply of drinking water within the permissible limit should be emphasized.