Abstract
Groundwater arsenic (As) contamination is a health threat for millions of people in the Gangetic plains of India. It is, therefore, critical to understand the mechanism of As enrichment to reduce the As exposure. Geochemical analysis of 30 groundwater samples collected across the banks of River Sharda was performed for the identification of major geochemical processes controlling groundwater geochemistry. Shallow wells (3-10 m) are found to be contaminated with As and is confined to newer alluvium of Holocene age. The average temporal decline of the groundwater level was observed across 10 monitoring stations is 0.067 m/yr. Decreasing rainfall, lesser recharge and huge groundwater extraction for irrigation might have impacted the groundwater to flow faster, while the increase in temperature and weathering regime favoured arsenic mobilisation. The long-term trends of rainfall show a decline of 1.97 mm/yr and the temperature increase is observed to be 0.0049 degrees C/yr. These changes in rainfall and temperature also might have impacted the As mobilisation in groundwater. NO3- was found to be low in samples with low As concentrations, indicating the prevalence of reducing conditions. Whereas high concentrations of Fe were observed for high As samples, indicating their common source of origin. Also, the alkaline nature of aquifer and high concentrations of HCO3- might have contributed to As enrichment. Results from scatter plots and correlation matrix also support this sequential reduction leading to the reductive dissolution of iron oxyhydroxides and thus enriching the concentration of As in the groundwater.