Arsenic Enrichment in the Groundwater of Diphu, Northeast India: Coupled Application of Major Ion Chemistry, Speciation Modeling, and Multivariate Statistical Techniques

Abstract

An integrated evaluation was carried out to predict prevailing processes of arsenic enrichment in the groundwater of Diphu, Assam, through major ion chemistry, speciation modeling, and multivariate statistical technique. Thirty‐eight groundwater samples were collected in 2011 to represent pre‐ and post‐monsoon season. Saturation indices of minerals present in the groundwater were calculated using MINTEQA2 to understand the future perspective of As contamination. Silicate weathering, rock water interaction, and reverse ion exchange are identified as major hydrogeochemical processes governing the groundwater chemistry. It could be shown that the release of carbonic acid due to silicate weathering resulted in an increase of total dissolved solid and increase in pH in the pre‐monsoon. Carbonic acid was further diluted and became alkaline due to monsoon recharge. The Gibbs plot revealed some anthropogenic input for the release of anionic minerals apart from rock–water interaction. Shallow aquifers were found to be more contaminated with As. Oxidative dissolution was identified as one of the major arsenic releasing mechanisms but a strong correlation between As and Fe was not identified. Future scenarios seem to be susceptible for As enrichment as natural equilibrium with As containing minerals is not reached. The study highlights the advantages of coupled application of major ions, multivariate statistical analyses, and associated change in saturation conditions of groundwater for better understanding of the arsenic enrichment processes.