Deciphering Fresh and Saline Groundwater Interface in South Chennai Coastal Aquifer, Tamil Nadu, India

Abstract

The interface between fresh and saline groundwater was studied in south Chennai coastal aquifer, through ArcGIS software using hydrochemical parameters (Ca²⁺, Mg²⁺, Na⁺, K⁺, B³⁺, CO₃^2-, HCO₃^-, Cl^-, NO₃^- and SO₄^2-) of 22 groundwater samples which was collected twice during pre-monsoon (August 2011) and post-monsoon seasons (January 2012). It was found that groundwater was slightly acidic to alkaline, and more than 81.8% of groundwater samples had EC > 1,000 μS/cm in both the seasons. The dominant cations and anions of the study area are in the order of Na⁺>Ca²⁺>Mg²⁺>K⁺>B³⁺ and Cl^->HCO₃^->SO₄^2->NO₃^->CO₃^2-, respectively. The Piper trilinear diagram shows that the groundwater exhibits Na⁺ –Cl^-, Mixed Ca²⁺- Na⁺ -HCO₃^-, Mixed Ca²⁺ -Mg²⁺ -Cl^- and Ca²⁺ -HCO₃^- hydrochemical facies. Gibbs diagram shows that the groundwater samples falls from freshwater to saline water. Chloro-Alkaline indices 1, 2 calculations shows that 100% of groundwater samples are negative, thus indicates exchange of Mg²⁺ and Ca²⁺ from water with Na⁺ and K⁺ of the rocks. The fresh and saline groundwater interface has been deciphered varies from 950 m in highly populated region to 250 m in partially populated region from the shoreline in pre-monsoon season and from 550 m in highly populated region to100 m in partially populated region from the shoreline in post-monsoon season. The interface is moving towards the inland due to the over exploitation of groundwater for various purposes, which disturbed the hydrodynamic balance of the region. It is inferred that the region which is highly populated is more intruded compared to partially populated area due to the over exploitation of groundwater. It’s an important issue to protect and preserve the groundwater resources from further depletion/contamination.