SPATIAL DISTRIBUTION, GEOCHEMICAL BEHAVIOUR, AND MOBILIZATION MECHANISMS OF ARSENIC IN THE AQUIFERS OF UPPER AND MIDDLE GANGETIC PLAINS, INDIA

Abstract

The Gangetic basin, covering an area of around 1.06 million square km (~26% of India`s landmass), is India's principal groundwater source, supplying approximately one-third of the country's 27 million wells. The vast majority of the basin area comprises the Gangetic Plain, the most extensive alluvial plain globally. Arsenic (As) is considered one of the most significant geogenic contaminants in the groundwater of the Gangetic Plain. Since the initial investigations of As in the groundwater of the Gangetic Plain, numerous studies have been conducted on the distribution, occurrences, and mobilization processes of As in groundwater. However, it is worth noting that most of these studies have focused on the lower Gangetic Plain (LGP) of West Bengal, followed by the middle Gangetic Plain (MGP) of Bihar, and in a few areas of Eastern Uttar Pradesh in MGP. Nevertheless, a large region in the MGP and upper Gangetic Plain (UGP) of the states of Uttar Pradesh and Uttarakhand has remained unexplored concerning As contamination in groundwater, along with several unexplained questions regarding the geochemical behavior and fate of As, mechanisms of mobilization, and geochemical and hydrogeological factors controlling the mobility of As in the aquifers of these regions. Furthermore, the World Health Organization (WHO) has recently increased the provisional recommended value (pGV) for manganese (Mn) in groundwater to 80 μg/L. This change has brought attention to the growing concern about Mn contamination of drinking water resources in the region. In order to address Mn contamination in the drinking water resources of the Gangetic Plain, this revised recommendation emphasizes the significance of increased vigilance and monitoring. Therefore, this study was conducted to examine the spatial distribution of As, Mn, and other redox-sensitive species and the processes regulating their mobilization in groundwater using geochemical, isotopic, and several statistical approaches. The study also focused on evaluating the hydrogeochemical characteristics and quality of groundwater in different regions of the Gangetic Plain. This study also tried to investigate the source of groundwater recharge and discharge in the region, the influence of recharge and discharge on contamination mobilization, geochemical evolution, rock-water interaction, and the interaction between surface and groundwater.