Vulnerability of low-arsenic aquifers to municipal pumping in Bangladesh

• Dhaka pumping is limiting access to safe drinking water in surrounding rural areas.
• Large vertical hydraulic gradients were observed ∼30 km away from pumping center.
• Modeled vertical recharge between shallow and deep aquifers was 0.21 m/yr.
• Estimated vertical movement of high arsenic water from shallow aquifers is 2–5 cm/yr.

SummarySandy aquifers deposited >12,000 years ago, some as shallow as 30 m, have provided a reliable supply of low-arsenic (As) drinking water in rural Bangladesh. This study concerns the potential risk of contaminating these aquifers in areas surrounding the city of Dhaka where hydraulic heads in aquifers >150 m deep have dropped by 70 m in a few decades due to municipal pumping. Water levels measured continuously from 2012 to 2014 in 12 deep (>150 m), 3 intermediate (90–150 m) and 6 shallow (<90 m) community wells, 1 shallow private well, and 1 river piezometer show that the resulting drawdown cone extends 15–35 km east of Dhaka. Water levels in 4 low-As community wells within the 62–147 m depth range closest to Dhaka were inaccessible by suction for up to a third of the year. Lateral hydraulic gradients in the deep aquifer system ranged from 1.7 × 10−4 to 3.7 × 10−4 indicating flow towards Dhaka throughout 2012–2014. Vertical recharge on the edge of the drawdown cone was estimated at 0.21 ± 0.06 m/yr. The data suggest that continued municipal pumping in Dhaka could eventually contaminate some relatively shallow community wells.

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