Coastal aquifers are increasingly threatened by seawater intrusion due to increased urbanization, groundwater exploitation, and global sea-level rise. A total of 161 ground water samples were collected during May 2017. Among the 13 blocks of Cuddalore district, only 4 coastal blocks viz., Parangipettai, Kumaratchi, Kurinjipadi and Bhuvangiri blocks were studied. Among the 4 coastal blocks studied (52 samples), Melathirukallipalai and Kavarapattu locations of Parangipettai block and Ammapettai, Erukkankattupadugai and Karuppur locations of Kumaratchi block of Cuddalore district were suspected for sea water intrusion based on their hydro geology parameters, molar ratios, piper plot facies, gibbs assessment. Bicarbonate and Chloride were the dominant anions, Magnesium and Sodium were the dominant cations found in the above mentioned locations. The ground water chemistry commonly found to be Ca-HCO3 type. However NaCl is also the dominant water facies in the above mentioned locations. Regarding salt water intrusion, the high Mg/Ca ratio (>5.4) may be indicative of salt water contamination in these locations. According to Cl/CO32- + HCO3- ratio (> 6.6) the screened locations have highly contaminated ground water (near sea water). Based on Na/Cl ratio (<0.86), the contamination may be due to marine source of origin.
Key words : Coastal blocks, ground water quality, Hydrology, ionic composition, piper plot..