Hydrogeochemistry of the paravanar river sub-basin, cuddalore district, Tamilnadu, India

To assess the groundwater quality of the Paravanar river basin, groundwater data were collected by conventional methods. Hydrogeochemical facies of groundwater of study area reveals fresh to brackish and alkaline in nature. Piper plot shows that most of the groundwater samples fall in the mixed field of Ca-Mg-Cl type. Using GIS mapping technique, major element concentration of groundwater has been interpolated and studied. Groundwater thematic maps on electrical conductivity (EC), hydrogen ion concentration, bicarbonates, chlorides and nitrates were prepared from the groundwater quality data. Different classes in thematic maps were categorized as i) good, ii) moderate and iii) poor with respect to groundwater quality. Northeast and southeast parts of the study area represent the doubtful water class regarding the concentration of EC to represent connate nature of water adjacent to the coast. NNE (North-North-East) and southern parts of the study area have pH ranging from 7 to 8 indicating acidic nature as they were from the weathered Cuddalore sandstone. As northern part of the study area is irrigated, fertilizer used for agriculture may be the source for increase in concentration of nitrates. Chloride clusters in the south central part of the study area from coast up to NLC mines and reveals the chloridization of aquifer in 48 years either due to upwelling of connate water from the deeper aquifer as a result of depressurization of Neyveli aquifer for the safe mining of lignite.