Arsenic distribution in the groundwater of the Central Gangetic plains of Uttar Pradesh, India

Abstract

Elevated arsenic (As) concentrations have recently been reported from groundwaters of the Holocene aquifers of the Indo-Gangetic plains in the states of Uttar Pradesh, Bihar and Jharkhand. This chapter reports about the nature of As contamination in groundwater in the Central Gangetic plain around the Ghazipur and Ballia districts, Uttar Pradesh, northern India. Groundwater samples were collected from a 2 km stretch in the flood plains of the Ganga and Ghagra rivers during two seasons for a one-year period. The samples were collected from shallow and deep tube wells and analyzed for hydrogeochemical parameters including the major anions and cations, and dissolved trace elements, including As. Arsenic concentrations in Ballia and Ghazipur were around 200 μg/l, albeit at some places below the detection limit. The As concentrations were very high in locations close to the river basin. They were also very high near an inland lake. Concentration of As were found to be moderate to low in the interior flood plains between these two basins. Groundwater As in these districts showed that intermediate aquifers have more As compared to deep and shallow aquifers. It was observed that As concentrations in groundwater were comparatively low in most places, expect for few locations in Ghazipur, where it exceeded 200 μg/l. The correlation between Fe and As was low, and sulfate concentrations in groundwater were relatively low. The shallow aquifers seem to be particularly at risk, due to the prevailing geochemical conditions in which oxidized and reduced waters mix, where the amount of sulfate, available for microbial reduction, seems to be limited. Further detailed study is needed in these two districts to obtain an insight into the precise geochemical processes occurring and controlling the As concentration in groundwaters.