Multivariate statistics and hydrogeochemistry of deep groundwater at southwestern part of Bangladesh

Multivariate statistics and GIS alone with geochemical modeling were applied to investigate the hydro-geochemical characteristics of groundwater and their spatial distribution in the deep aquifer system of Bagherpara Upazila, Bangladesh. This Upazila consists of an area of 308.3 km(2) and local people mostly rely on groundwater to meet the drinking water requirements. Water samples from one hundred randomly selected deep tube wells (152–198 m) were collected and analyzed for 14 water quality parameters to characterize the hydro-geochemical properties. The groundwater shows slight alkaline in nature throughout the study area. Most of the water samples were turbid and 68% of them failed to meet the drinking water quality standard prescribed by the World Health Organization (WHO). TDS concentration ranges between 280 mg/L and 1040 mg/L, with a mean value of 446.20 (±122.19) mg/L. The general order of cation and anion along the study area were Ca(2+)>Mg(2+)>Na(+)>K(+) and HCO(3)(-)>Cl(−)>PO(4)(3-)>SO(4)(2-)>NO(3)(-) respectively. Carbonate weathering is the dominant process for releasing ions in groundwater. Besides, the ion exchange process is active in the study area, which leads to the reduction of Na(+) ions. Gibb's plot suggests a rock dominance inheritance controls the dissolution and precipitation of minerals along with the ion-exchange process, and ultimately dictates the groundwater chemistry. Besides, the Piper diagram showed that Ca(2+)-Mg(2+)-SO(4)(2-) is the dominant water type in 65% of the samples followed by Ca(2+)-Mg(2+)–HCO(3)(-) water type (35%). The abundance of Ca(2+) and Mg(2+) ions and the alkaline nature of groundwater indicate mixed geochemical facies and reverse exchange reactions. The principal component analysis (PCA) reveals that weathering and leaching of host rocks was the main natural source, while municipal solid waste dumping, sewage discharge, and fertilizer application could be other anthropogenic factors that affect the groundwater geochemistry. In fine, the chemical characteristics of groundwater were acquired through rock dissolution, percolation, and reverse exchange process.