The Tista is a Trans-Himalayan river that flows through Sikkim and West Bengal states of India and Rangpur division of Bangladesh and finally falls into the Brahmaputra River. The presence of numerous abandoned channels with various degrees of aggradations indicates large migrations of the Tista River. The pH value of groundwater varies from 6.20 to 7.40 which indicate the slightly alkaline to acidic nature of the studied aquifers. The mean abundance of major cations is Na⁺ > Ca⁺² > Mg⁺² > K⁺, whereas the major anions is HCO₃⁻ > Cl⁻ > SO₄⁻². Among the cations, Na⁺ is the dominant and K⁺ is the lowest constituents, whereas HCO₃⁻ is most abundant and SO₄⁻² is the minor constituents in anions. The hydrochemical facies of groundwater show that sodium, sodium–magnesium, sodium–calcium, sodium–magnesium–calcium and sodium–calcium–magnesium are cation facies and chloride–bicarbonate, bicarbonate–chloride and bicarbonate are anion facies. Correlating with WHO (Guidelines for drinking-water quality, 1, World Health Organisation, Geneva, 1997) and EQS (Environmental quality standard, Department of Environment, Bangladesh, 1989) guideline values for drinking water and public health, it may be concluded that the groundwater of the study area is suitable for all drinking and domestic purposes, where only three samples exceed the maximum allowable limit of potassium. Based on total hardness, SAR, RSC, PI, SSP and MH values, it can be summarized that the groundwater of the investigated area is suitable for irrigation purpose. On the basis of Australian and UNESCO standard, the groundwater of the study area is also suitable for livestock purposes. The Rangpur area is hydrogeologically active by the processes like ion exchange and dissolution. Ca²⁺, Mg²⁺ and HCO₃⁻ are produced by the dissolution of limestone and dolomite.

The geochemical analysis of the shallow aquifer sediments of the area of investigation reveals that they are acidic in nature. The mean electrical conductivity of the deposits is 1.16 dS/m that indicates very low or negligible effects of salinity of the sediments of the Rangpur division. The median values of the concentrations of total organic carbon, total nitrogen and sulphur are 0.20%, 0.02% and 58.68 mg/kg, respectively. The trend of the average heavy metal concentrations of the investigated area can be shown as Fe > As > Cu > Zn. The average concentrations of arsenic of the sediments of the study area are 3.52 mg/kg. Sulphur is significantly, positively correlated with copper and zinc (p < 0.05) and insignificantly and positively correlated with arsenic content of the sediments that indicates that the copper and zinc occur as sulphide minerals. The mean concentrations of arsenic in the groundwater are 1.1793 μg/L. The concentration of all the water samples is below the permissible limit of World Health Organization (10 μg/L). The arsenic content of groundwater shows the positive correlations with the arsenic, iron and copper concentrations of the sediments. This implies that the arsenic of groundwater derived from the geogenic source, like the dissolution of arsenic bearing minerals of the aquifer sediments—pyrite and arsenopyrite. The acidic nature, texture and minor quantities of total organic carbon are the factors that also influence the low arsenic enrichment in the investigated sediments and its release to the groundwater. The contemporary arsenic specification research works showed that As(III) the most common species in natural water and foodstuffs and the arsenic is inorganic from source in Bangladesh.

The present research work deals with the petrographic analysis of the Tista sand deposits which is exposed along the river bank and point bars. The constituent minerals of the sand deposits are quartz (73.18%), microcline (8.10%), orthoclase (0.15%), plagioclase (1.16%), lithic grains (1.37%), muscovite (6.59%), biotite (3.67%), heavy minerals, organic matters, minor amounts of matrix whereas fine-grained quartz and clay constitute the matrix materials. The heavy minerals include pyroxene, amphiboles, zircon, tourmaline, garnet, chlorite and opaque minerals. The major minerals and the lithic grains can be expressed as quartz>feldspar>lithic grains using the QFL ternary diagram. Among the heavy minerals, garnet is the most abundant mineral. The presence of magnetite was established using its magnetic susceptibility. Ninety-two percent of the sand specimens have the mineralogical index value ranging from 80 to 100, which suggests that the Tista sand deposits were derived from an extremely weathered condition. The QPK (Quartz-Plagioclase-K-feldspar) ternary plot reveals that all the sand samples fall near the Quartz-apex and the prevalence of more stable K-feldspar over the less steady plagioclase feldspar. The bivariate diagram of ln(Q/R) versus ln(Q/F) suggests the metamorphic provenance for the investigated sand deposits. The Q/(F+L) vs Qp/(F+L) plot indicates that the humid climatic conditions prevailed during the deposition these sand deposits.