Hydrogeochemistry and multivariate statistical analysis of groundwater quality of Tista alluvial fan, Bangladesh.

The present research work is conducted with the water quality data of the Tista alluvial fan of the summer season. The lowered values of groundwater pH were documented which is suggestive of chemical breakdown of carbonic acid and lack of alkaline materials in the aquifer which results from the long-term weathering of the sediments. From the plot of the Schoeller diagram, it can be summarized that among the cations Na predominates over K, Ca, and Mg, and HCO₃¹⁻ is the most dominant anion of the studied groundwater in summer. The summer groundwater specimens are of NaHCO₃ type. The reverse ion exchange is identified as the prime hydrochemical process that governs the hydrogeochemistry of the Tista alluvial plain. Ninety-two percent of the groundwater samples have higher K content than the recommended by WHO in 1997. The mean total hardness value is 104.92 mg/L and the total hardness shows a strongly significant positive association with the HCO₃¹⁻ anion, indicating the temporary hardness of the groundwater. The principal component analysis (PCA) recognizes that three principal components incorporate 76.035% of the total variance. Principal component-I specifies the alkaline state of groundwater where dissolved CO₂ plays a vital role. Principal component-II is marked by negative loading of pH with the positive loading of SO₄²⁻ and HCO₃¹⁻ anions, and it is favored by the decomposition of organic materials in the study area. Principal component-III is distinguished by the elevated levels of Cl¹⁻ ions in the distal part of the fan. The cluster analysis (CA) classifies the groundwater samples into two categories, namely cluster-1 and cluster-2. Cluster-1 contains three groundwater stations and is characterized by the higher values of total dissolved solids (TDS) in Sundarganj Upazila. Cluster-2 is composed of ten groundwater wells in which the levels of K, Ca, Na, and SO₄ are high. [ABSTRACT FROM AUTHOR]