Arsenic in Bangladesh Groundwater: Focus on Deep Aquifer for Mitigation and Management

Since first detection in 1993, a large number of investigations on local to national scales have been carried out covering various aspects of arsenic occurrences in Bangladesh groundwater. The extent of the problem is well known where at least 29 million peoples are exposed to arsenic above Bangladesh national drinking water limit of 0.05 mg/L. As exposure through drinking water is the major route, efforts are being focused on providing arsenic safe drinking water to the exposed population. Various different alternative safe water options based on rainwater, surface and groundwater are being implemented. Deep tube wells, pumping from various depths depending on the local geological conditions, are found to be the most useful in providing safe water on a sustainable basis with minimum potential for risk substitution.

The BGS/DPHE National Hydrochemical Survey for the first time reported the occurrences of arsenic safe water at aquifers deeper than 150m. However, most of the deep samples for the survey were collected from the coastal regions. Since then, other surveys came out with findings that depth was not the only criteria for arsenic safe drinking water; rather the local geology plays a vital role in it. It has been found over most of the country that the Pleistocene sediments, irrespective of depth occurrences, provide safe water. Also the localized oxidized sediments at shallower depths provide arsenic safe water. However, this aquifer in many places contains high Manganese. Also in some parts the deeper aquifer contains relatively higher concentrations of other trace elements such as Boron. Apart from quality issues, there are number of other hydrogeological factors which need to be understood well in order to abstract safe water from the deep aquifer on a sustainable basis. The paper would focus on the key hydrogeological and management issues related to deep groundwater in Bangladesh.