Assessment of groundwater quality using Entropy-Weighted Quality Index (EWQI) and multivariate statistical techniques in Central Ganga plain, India

The present study aims to identify the quality of groundwater using integrated multivariate statistical approach and Entropy-Weighted Quality Index (EWQI) in Mathura city of Uttar Pradesh. A systematic sampling of a total of 96 samples was carried out in two consecutive seasons and tested for major ions analysis using standard procedures. The groundwater is falling in brackish category, alkaline and classified as hard to very hard type which is somewhat unique for an area falling within Central Ganga Plains. The relationship between electrical conductivity and Cl−/SO42− demonstrates an increase in salinity proportional to the ratio confirming evaporitic dissolution as the dominant process controlling the groundwater chemistry. The correlation coefficient revealed that TDS are strongly positive correlated with all salt including Na, Cl and SO4 and moderately positive correlated with Ca, hardness and K in both seasons. This suggested that the salinity is much more related to geogenic environment consisting of halite (NaCl), Sylvite (KCl) and Gypsum (CaSO4) mineral. The graphical presentation reveals that Na-K-Cl-SO4 is the dominant hydrochemical facies of groundwater. The results of various multivariate statistical techniques such as principle component analysis, hierarchical cluster analysis and correlation coefficient demonstrated groundwater quality to be controlled mainly by geogenic and to some extent anthropogenic factors. The Entropy-Weighted Quality Index (EWQI) using entropy values comprising numerous hydrochemical variables has been employed and proved to be more feasible WQI method due to more extensive computation. According to the EWQI, majority of samples displayed at rank 3 and medium groundwater quality in both the seasons. The extreme northern, western and eastern parts of regions have elevated EWQI values. These areas certainly require more attention for groundwater protection in future.