Hydrochemical characteristics and quality assessment of shallow groundwater in a coastal area of Southwest Bangladesh

In this study, the hydrochemical characteristics of shallow groundwater in a coastal region (Khulna) of southwest Bangladesh have been evaluated based on different indices for drinking and irrigation uses. Water samples were collected from 26 boreholes and analyzed for major cations and anions. Other physico-chemical parameters like pH, electrical conductivity (EC), and total dissolved solids were also measured. Most groundwater is slightly alkaline and largely varies in chemical composition, e.g. EC ranges from 962 to 9,370 μs/cm. The abundance of the major ions is as follows: Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ = Cl⁻ > HCO₃ ⁻ > SO₄ ²⁻ > NO₃ ⁻. Interpretation of analytical data shows two major hydrochemical facies (Na⁺–K⁺–Cl⁻–SO₄ ²⁻ and Na⁺–K⁺–HCO₃ ⁻) in the study area. Salinity, total hardness, and sodium percentage (Na%) indicate that most of the groundwater samples are not suitable for irrigation as well as for domestic purposes and far from drinking water standard. Results suggest that the brackish nature in most of the groundwaters is due to the seawater influence and hydrogeochemical processes.