ABSTRACT
ABSTRACT: This study is based on the concept that lack of dissolved oxygen (DO) at or below the water table and water extraction (Q) through shallow irrigation wells at a rate greater than the aquifer recharge rate are the main causes of arsenic release in the groundwater of Bangladesh. This study identified the hydrogeochemical processes related to shortage of DO that eventually produce high arsenic concentrations and their migration into the groundwater systems. The existing theories of arsenic release by oxidation and reduction in the context of dissolved oxygen shortage in recharging groundwater were studied. Both numerical and thermodynamic analyses were used to demonstrate how oxidation theory of arsenic release is inadequate to explain the release of arsenic into the groundwater of Bangladesh. This study quantified the amount of dissolved oxygen level in deeper layers of the aquifer and their relation to the variations in redox potential values and arsenic release processes. It also analyzed groundwater velocity and flow patterns to establish a link between dissolved oxygen shortage and arsenic release into the groundwater. On the basis of the findings, it was concluded that shortage of dissolved oxygen in recharging water is the most likely the root cause of arsenic occurrence in Bangladesh groundwater.
