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

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 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.

A partially coupled hydro-mechanical analysis of the Bengal Aquifer System under hydrological loading

“…In terms of the extent to which piezometer water levels indicate recharge and drainage, it is only where there is a rapid hydraulic connection between the piezometer and the water table that the piezometer will be sensitive to head change at the water table and therefore to changes in unconfined storage. If a piezometer is hydraulically isolated from surface water and/or the water table and is beyond other transient hydraulic influences, it can respond to changes in the weight of the TWS load, acting as a geological weighing lysimeter (van der Kamp and Maathuis, 1991;Smith et al, 2017). In this case, where the changing load is due to a moving water table, knowledge of the loading efficiency allows the load measurement to be converted into an estimate of recharge and discharge.…”

“…Under these conditions, porewater pressures are determined by changes to surface mechanical loading alone, and changes in groundwater head may be taken as a measure of changes in TWS mechanical loading above the surface of the aquifer. This is the conceptual basis for geological weighing lysimetry (van der Schmidt, 1997, 2017;Campbell, 1994, 2007) as used in diverse environments to determine TWS at the scale of individual catchments (Marin et al, 2010;Lambert et al, 2013;Barr et al, 2000;Smith et al, 2017). Geological weighing lysimetry has been suggested as suitable for mapping the variability of TWS within the Bengal Basin (Burgess et al, 2017;Bardsley and Campbell, 2000), complementary to basin-scale estimates based on the Gravity and Climate Recovery Experiment (GRACE) satellite mission (Tapley et al, 2004;Tiwari et al, 2009;Shamsudduha et al, 2012).…”

Multi-hazard Groundwater Risks to Water Supply from Shallow Depths: Challenges to Achieving the Sustainable Development Goals in Bangladesh

“…About 20% of these wells are considered deep (> 150 mbgl) wells (DPHE 2016). However, there are concerns of potential contamination of deep groundwater due to ingress of As and salinity from shallow depths (Shamsudduha et al 2018). Further, improper well-sitting has been documented during extensive deep tubewell installation campaigns (Mondal et al 2014;van Geen et al 2016).…”

Modeling solute transport in karst fissure dual porosity system and application: A case study in an arsenic contamination site

“…Some researchers have established different risk assessment models to evaluate the health risks of arsenic pollution in groundwater [8,9]. As for the migration rule of arsenic in groundwater, some studies considered that iron/manganese oxides, organic matter, and REDOX conditions are the main factors affecting the migration and transformation of arsenic in water bodies [10][11][12][13]. Local conditions/geometry strongly affect the distribution of fractures and thus porosity, permeability and elastic parameters [14,15].…”