Hydrochemical evaluation of groundwater quality of the Tista floodplain, Rangpur, Bangladesh

Abstract 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.