Salinity Ingress in Phreatic Aquifer of Coastal Maharashtra State, India

Abstract

Maharashtra a coastal state of the western 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, analytical study was carried out to decipher the level of salinity intrusion of the shallow coastal aquifer inthe coastal Maharashtra.

The present research work was carried out for the assessment of groundwater contamination 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 in the month of May 2017. For the assessment of the sea water intrusion levels, different 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 of the area selected for this study is slightly 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 fit for various domestic and irrigation purposes. Though salinity can be imparted to groundwater in many ways, it is mainly due to sea water ingress and waste water including industrial effluents in the area selected for the study. 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.