Salinity Intrusion from Tidal Recharge and its Impact on Groundwater Quality in Goa State

Chemical analyses of water samples collected from streams, borewells and dugwells tapping a shallow zonc in Goa indicate that some groundwater occurring in dug wells as well as bore wells is influenced by salinity due to tidal recharge along the river Chapora near the coast. The contamination of groundwater is more pronounced in dry season than in wet season and in areas close to the stream courses. Morcover, the groundwater adjacent to stream course in the NE of Panjim is polluted with domestic sewage in addition to high salinity. The ionic ratios, such as Na⁺/Cl^-, Cl^-/CO₃^2- + HCO₃^-, Na⁺/ca²⁺ + Mg²⁺ and Br^-/cl^- of Typc III waters, in which strong acids and alkalies exceed weak acids and alkaline earths respectively, are comparable to the ionic ratios of average seawater. However, some well waters have shown secondary salinity, which can be attributed to reverse ion exchange undergone by the intrusive seawater before meeting the groundwater. Fluoride contents of these contaminated waters which is higher than the average fluoride concentration in the groundwater of the area also suggest the mixing of intrusive water with fresh groundwater.