Assessment of ground water quality in the vicinity of Sylhet City, Bangladesh: a multivariate analysis

Abstract

Water, the most naturally abundant and the simplest molecule on the earth, is crucial for the existence of all flora and fauna on this planet. Groundwater chemical composition can change the suitability of the aquifer system. The aim of the study was to provide an evaluation of water quality with respect to different water quality parameters in the north-east part of Bangladesh using multivariate techniques. It also tried to identify the vital sources that control the groundwater resources in the aquifer. All samples were collected during the pre-monsoon season in March 2019 from 20 pumps of Sylhet City Corporation area. Correlation analysis has been used to assess the overall groundwater quality and the degree of the linear relationship between parameters. Multivariate statistical techniques have been used to interpret the water quality of the selected pumps and to provide some meaningful results that are not possible while investigating the data at a glance. The average concentrations of major ions in groundwater of Sylhet City Corporation area are in the following order: cations—Magnesium (28.43) > Sodium (11.45) > Calcium (8.47) > Potassium (1.36); while, anions—Bicarbonate (87.70) > Chloride (37.20) > Sulfate (1.80) > Nitrate (0.95). The correlation matrix shows that the basic ionic chemistry is influenced by pH, EC, TDS, K+, Na+, Mg2+, and SO42−. These characteristics of the water samples indicate that, in addition to fresh recharge water of CaHCO3 type, the groundwater are dominated by the dolomite (CaMg(CO3)2), calcite (CaCO3) and halite (NaCl) rock-forming minerals. PCA extracted three components, which are accountable for the data composition explaining 71% of the total variance of the data set and allowed to set the selected parameters according to regular features as well as to evaluate the frequency of each group on the overall variation in water quality of Sylhet City Corporation area. The factors have been identified as “freshwater and halite minerals interaction”, “anthropogenic influences”, and “anthropogenic-rocks interaction effect”. Hierarchical cluster analysis grouped the 20 sampling stations into five groups, the values of pH and HCO3− concentration increase gradually from cluster 1 to cluster 5, i.e., from the eastern part to the western part of the city. The western part is relatively on the downward side and thus, the recharge water of CaHCO3 type is comparatively affluent in this area.