Hydrochemical Characteristics of Groundwater of Deeper Aquifers and GIS Based Assessment of Groundwater Quality for Domestic and Irrigational Purposes in Pondicherry Region of Union Territory of Pondicherry, South India

ABSTRACT The study investigates the hydrochemical characteristics of groundwater from one of the main coastal tourist destinations in India, Pondicherry. The Pondicherry Region comprises 293 Km2, which lies in the south-eastern coastline, surrounded by the Bay of Bengal. A total of 62 samples were collected from the various locations covering the entire study region during May 2022 (pre-monsoon). The basic parameters such as pH, EC, TH, TDS, major cations (Ca, Mg, Na, K), and anions (HCO3, CO3, Cl, NO3, SO4) were analysed by using the standard titrimetric method by APHA guidelines, an ICP-mass spectrometer, a flame photometer, and ion chromatography. The irrigation suitability was estimated using statistical methods and a correlation matrix. The study revealed that the Cl- has a very high correlation (0.93) with Na+, revealing the existence of marine water intrusion. In order to visualise the irrigation suitability distribution over the study region from the USSL salinity diagram and Wilcox diagram, respectively, 69.8% of the sample has SAR low and EC high, and 46.1% is in the good to permissible category. Furthermore, in Donne’s chart for permeability index, the samples fall in classes 1 and 2 combined, indicating the water is suitable for irrigational purposes. The hydrochemical development of groundwater is identified by using Gibb’s plot and finds that it is dominated by ion exchange and rock-water interactions, shaped by the aquifer framework geology and other climatic factors.