Comparative study on groundwater quality assessment of Chennai District, Tamil Nadu during 2019-2020

• Groundwater composition is significantly affected by geogenic processes. • Major ions signature of groundwater reveals the nature of hydrogeochemical processes controlling the groundwater chemistry. • Potability of groundwater was assessed through the evaluation of Water Quality Index. • Water-rock interaction is the major geogenic process affecting the groundwater chemistry. The groundwater usage for household, industrial and agricultural needs is largely depends upon the nature and composition of various dissolved components present in the water. A comparison of groundwater quality of Chennai district in 2019 and 2020 for its potability and its hydrogeochemical characteristics were studied using the physicochemical data of representative samples from 36 observation wells obtained during pre monsoon and post monsoon seasons. The chosen wells are spatially distributed in the study region. The present work was carried out using the water quality data consisting of various physicochemical parameters and major ions concentration pertaining to groundwater analysis of the study location obtained from State Groundwater and Surface Water Resources Data Centre (SGSRDC), Taramani, Chennai, India. Water quality parameters such as pH, total dissolved solids(TDS), total hardness(TH), total alkalinity(TA), Ca 2+ , Mg 2+ , Cl ‒ , SO 4 2‒ , and NO 3 ‒ ,were used to calculate the water quality index (WQI) by weighted arithmetic method. The groundwater quality is ascertained from the calculated WQI values with reference to Bureau of Indian Standards (BIS). The results of WQI calculation reveals that in the pre monsoon period of both 2019 and 2020, around 30 % samples fall under good category and 55 % samples fall under poor quality. In the post monsoon period of 2019, 70 % samples are of good quality, whereas for 2020, 61 % samples are of poor quality. Correlation analysis of water quality parameters and bivariant plots of major ions were plotted to decipher the hydrogeochemical characteristics of groundwater. TDS, TH and electrical conductivity (EC) exhibits a strong positive correlations with Ca 2+ , Mg 2+ , Na + , Cl - and SO 4 2- ions. The Piper diagrams of the ground water samples of the study area reveal its hydrochemical facies as Na-Cl type. The Gibbs diagram of the groundwater samples shows that water-rock interactions and evaporation are the predominant factors in controlling the ground water chemistry.