Remediation potential of arsenic in the alluvial aquifers in the Bengal Basin: insights from simulations and time estimates

Arsenic is found in significant quantities within the alluvial aquifers. Bangladesh heavily relies on the alluvial aquifers of the Bengal Basin as a source of irrigation and drinking water. Due to the flat topography, arsenic within an aquifer is not easily flushed out of the system. Additionally, continuous, unregulated pumping causes arsenic from deeper aquifers to migrate to shallower levels. This study simulates groundwater and contaminant transport in the alluvial aquifers of the Bengal Basin by comparison between two scenarios prior to human intervention with different sea levels, employing a combination of MODFLOW, MODPATH and MT3DMS. The simulations demonstrate that the hydraulic gradient and flow rates were higher during periods of considerably lower sea levels than they are at present. Additionally, it would require 5,600 years for the Holocene aquifer and 3,300 years for the Last Glacial Period aquifer to flush arsenic to the Bangladesh standard concentrations in drinking water in a 100-m-thick contaminated aquifer. This implies that if the sea level continues to rise with climate change, it will be difficult to remove arsenic from the alluvial aquifers in the Bengal Basin by natural flushing, which means artificial interventions need to be done in that region in the interest of the nation's health.