Abstract
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 km2 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.
Highlights
The extensive and excessive occurrence of arsenic (As) in groundwater of the Bengal Aquifer System (BAS) in Bangladesh (Fendorf et al 2010), mostly within 100 m of the ground surface across the floodplains of the Ganges, Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Brahmaputra and Meghna Rivers, is resulting in a national public health catastrophe (Ravenscroft et al 2009; Smith et al 2000)
The pre-development pattern is of long groundwater flow paths deriving from recharge in the distant hilly regions at the basin margins
We find that the simulated flow path direction and length are highly sensitive to groundwater abstraction, aquifer properties, Kh/Kv anisotropy, and the distribution of low-permeable layers
Summary
Groundwater from shallow hand-pumped tube wells (HTWs) installed at a few tens of meters to 150 m belowground level (bgl) is used for domestic supply by 80% of the population (BGS and DPHE 2001; Rahman and Ravenscroft 2003). Most of these tube wells are privately owned and are operated throughout the year at a very low discharge rate, < 1 L s− 1 (Ali 2003); approximately, 27% provide water exceeding the Bangladesh national limit of As in drinking water (50 μg L− 1), and 46% exceed the World Health Organization guideline value (10 μg L− 1). By 2005, a total of 150,000 deep hand-pumped tube wells (> 150 m bgl) had been installed throughout Bangladesh
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