GIS Based Groundwater Quality Assessment of Vattamalaikarai Basin, Tamil Nadu, India

A detailed GIS based study on hydrochemistry of groundwater in Vattamalaikarai Basin, Tamil Nadu, India has been carried out to assess the quality of groundwater for determining its suitability for drinking purpose. Further, the spatial variation of various groundwater quality parameters over the basin has also been studied for January 2008. The area is underlained by crystalline rocks of peninsular gneissic complex, comprising of hornblende-biotite-gneiss and charnokite. Black, alluvial, and calcareous soils are major soil types in this region. Fifty nine groundwater samples spread over the basin have been collected from open and tube wells during January 2008. The physicochemical parameters have been compared with the standard guideline values as recommended by the WHO for drinking and public health. The abundance of major ions in groundwater is in the following order: Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ = Cl^- > SO₄^2- > HCO₃^- > NO₃^- > CO₃^2-. TDS widely varied from 124 to 4270 mg/L with an average value of 1422 mg/L, and at 24 locations it exceeds the maximum allowable limit of 1500 mg/L leading to unsuitability of groundwater in nearly 40% of the total basin area. TDS exhibits good positive correlation with Na⁺, Mg²⁺ and Cl^-. Groundwater of the basin belongs to hard to very hard water category since the total hardness (TH) exceeds the permissible limit of 500 mg/L prescribed for drinking water. Nitrate concentration in groundwater also widely varies from 0 mg/l to 647 mg/L with an average value of 125 mg/L. Forty four well samples out of 59 exceed the maximum allowable limit of 45 mg/L (60% of the total basin area). Fluoride is also high (> 1.5 mg/L) in groundwater at 17 locations, which may cause dental fluorosis.