Assessment of hydrogeochemistry and arsenic contamination in groundwater of Bahraich District, Uttar Pradesh, India

The paper presents the assessment of geochemical characteristics of groundwater and evaluates the suitability of groundwater for drinking purpose using water quality index (WQI) in the Bahraich district of Uttar Pradesh state in India. Forty samples from groundwater and five samples from surface water along the Ghagra River are collected during the post-monsoon season. All samples are analyzed for physical parameters pH, electrical conductivity (EC), dissolved oxygen (DO), and oxidation–reduction potential (ORP); cations (Na+, Ca2+, K+, Mg2+); anions (Cl−, SO42−, HCO3−, and NO3−); and trace metals (Fe, Mn, Al, As, Pb, Zn, and Cu). Results are compared with the BIS and WHO standards for the drinking purpose, which show elevated trace metal concentration in some of the samples. The arsenic concentration is found exceeding the WHO recommended value of 10 μg/l in about 42% groundwater samples. Fe and Mn are also found in higher concentration than the permissible limits. The WQI of samples range between 45 and 1219 with an average of 273. More than 80% samples are found under the category of poor or unfit water for drinking purpose. Hydrogeochemical facies are also studied by the Piper diagram which shows the dominance of Ca–Cl, Mg-Cl followed by Na-Cl, Mg-SO4, and Ca-HCO3. The relative order of abundance of cations and anions is found in the decreasing order as Ca2+  > Mg2+  > Na+  > K+ and Cl−  > SO42−  > HCO3−, respectively. Gibbs diagram indicates the predominance of rock-water interaction in controlling the groundwater chemistry. The isotopic signature shows the predominance of local precipitation over evaporation and groundwater recharge and supports the geogenic nature of arsenic contamination in the study area.