Arsenic enrichment in groundwater in southern flood plain of Ganga-Son interfluves

Abstract

Arsenic contamination is extensively present in the Holocene alluvial aquifer of middle plain of Ganga. Arsenic concentration in most of the public supply networks exceeds the maximum allowable limit of 50 μg/l (BIS 2003) for drinking water. The primary purpose of this work is to find out the hydrochemical characteristic of groundwater and identify the process of controlling the arsenic contamination and possible relationship among arsenic and other elements through factor analysis. High concentrations of As, Fe and NO3 are responsible due to the redox process and anthropogenic activity. The depth profile of As shows that As depleted with depth and concentration of NO3 is low associated with higher As. Piper Trilinear diagram shows hydrochemical facies categorize into three groups: (a) Ca–HCO3, (b) Na–Ca–HCO3 and (c) Na–HCO3. Dominance of Ca–HCO3 over SO4 + Cl indicates that high recharge phenomena is operated in groundwater sample of study area. According to the Eh-pH diagram, Arsenate (V) and Arsenite (III) are both type of species present in groundwater sample. The poor relationship between As and Fe indicates that, process of releasing As in groundwater are reduction of arseniferous iron hydroxide coupled to precipitation of Fe as FeCO3 when anoxic conditions develop during microbial oxidation of sedimentary organic matter. Multivariate statistical analysis reveals the relationship between different elements. Correlation matrix suggested that strong positive pair association between As–pH, NO3–Cl and Na–Cl etc. are responsible due to carbonate and silicate weathering with some anthropogenic activity. The present study shows that the As concentration in groundwater sample in the study area does not only make alarm but also calls for the immediate action.