Security of deep groundwater against arsenic contamination in the Bengal Aquifer System: a numerical modeling study in southeast Bangladesh

Across the floodplains of southern Bangladesh deep (> 150 m belowground level, bgl) groundwater within the Bengal Aquifer System (BAS) has become widely used for domestic water supply as a de facto mitigation response to the presence of excessive arsenic (As), exceeding the World Health Organization standard of 10 µg L − 1 , in shallow groundwater. Over the past 10 years, many hand-pumped tube wells and high-capacity municipal water-supply wells have been installed at this depth and at deeper regions of the BAS, which are almost uniformly free of excessive As. Concern for the security of the deep groundwater resource against possible invasion of As and saline water from shallow depths emphasizes the need for comparative assessments of groundwater abstraction strategies to guide water resource managers and policy makers. To this end, particle-tracking post-processing has been applied within a numerical groundwater flow model for an area of over 10,000 km 2 in southeastern Bangladesh, one of the regions where the As issue is most acute. Criteria for describing the security of deep groundwater abstraction strategies over a 100-year time frame have been applied to the model outcomes for a range of scenarios. Our analyses suggest that deep groundwater will remain secure against invasion of As across the entire region if it is restricted to domestic use, even under domestic demand projected for 2050. Our approach can be applied in other regions and in similar Asian mega-deltas where As contamination of groundwater is recognized as a grave concern for sustainable water resources development.