Salinity Ingress in Phreatic Aquifer of Coastal Maharashtra State, India

Abstract

Maharashtra is a coastal state on the west coast of India where six out of thirty five districts, namely Palghar, Thane, Raigad, Ratnagiri, Sindhudurg and Greater Mumbai are maritime. Being coastal area, the immediate effect of high groundwater development is sea water intrusion. Hence, an analysis was carried out to decipher the extent of salinity intrusion of the shallow coastal aquifer in the coastal Maharashtra.

The study was conducted with the objective to assess the extent of contamination of groundwater in the phreatic aquifers in the tidal backwater limits and adjacent to coast and estuaries. Geochemical characteristics, extent of salinity intrusion, drinking and irrigation suitability of the groundwater of the area were also assessed. Total 162 ground water samples from coastal part of Maharashtra were subjected to chemical analysis for 15 basic parameters during the month of May 2017. In order to differentiate and confirm the sea water intrusion, various ionic ratios like Ca:Mg, Na:Cl, Cl:CO₃ + HCO₃, were computed. Wilcox Diagram, EC Vs Cl plots, Pipers Trilinear diagram etc were also plotted for the interpretation of the results. Groundwater in the study area is mildly alkaline with pH range of 6.9 to 9.0 and electrical conductivity range from 61 to 29370 μS/cm. In general, water quality is good and suitable for domestic and irrigation uses. Though salinity can be imparted to groundwater in many ways, in the current study area it is mainly due to sea water ingress and waste water including industrial effluents. From the analysis it is found that about 2 to 10 km area from the coast and the inland tidal backwaters are affected from salinity intrusion.

Over-exploitation of groundwater, low seaward freshwater flow in rivers etc are the major reasons for sea water ingression. Regulation of groundwater development in the coastal area and adjacent to estuaries, maintaining adequate stream flow and stopping of river bed sand mining, construction of tidal regulators at suitable places and creating fresh water barrier through rainwater harvesting and groundwater recharge are essential to control further sea water intrusion in the area.