GROUNDWATER FLOW DYNAMICS AND ARSENIC MOBILIZATION IN MUNSHIGANJ, BANGLADESH

Widespread arsenic contamination of groundwater is a major concern in Bangladesh since the water supply, particularly in rural areas, is heavily dependent on groundwater. However, little work has been conducted in Bangladesh to understand the complex transient dynamics of groundwater flow, and the transport of arsenic and other solutes that control its mobility. A lumped-parameter hydrologic model of our field area indicates that: (1) the shallow aquifer acts primarily as a conduit for flow from ponds and rice fields to irrigation wells and rivers, and has little seasonal change in storage; (2) most inflow to the aquifer occurs during the dry season, and the monsoon contributes relatively little to the inflow since the aquifer storage is small; (3) because the increase in irrigation pumping and pond construction have changed the groundwater flow dynamics, arsenic concentrations are unlikely to be at steady-state. Extensive small-scale pump tests and one large-scale extended pump test have been carried out to understand the aquifer characteristics of our study area in Munshiganj. Results from a three-dimensional hydrological model suggests that groundwater irrigation has changed the flow dynamics in the area – not only by reducing the residence and travel times, but also by carrying solutes to particular depth from different sources and locations.