Vulnerability of low-arsenic aquifers to municipal pumping in Bangladesh

Abstract

Sandy 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 (>150m), 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.

Security of Deep Groundwater in the Coastal Bengal Basin Revealed by Tracers

“…At three locations (Khulna, Lakshmipur, and Digha) there has been decades of intensive pumping for drinking water. Downward hydraulic gradients between shallow and deep piezometers for Khulna and Lakshmipur (3 m and 5 m head difference, respectively, see supporting information) are comparable to downward gradients reported close to Dhaka (2–4.5 m) by Knappett et al (). With the exception of site 1 Digha (DI) and site 5 Khulna (KH), all sampled installations are purpose‐built, multilevel monitoring wells and included sites used in previous hydrogeological studies [sites 3 Sahishpur (SA), 2 Kamgachi (KM), and 9 Kachua (KA) and four newly constructed multilevel monitoring stations (sites 4 Gabura (GA), 6 Kuakata (KU), 7 Barisal (BA), and 8 Lakshmipur (LA)] (BWDB, , ).…”

“…At three locations (Khulna, Lakshmipur, and Digha) there has been decades of intensive pumping for drinking water. Downward hydraulic gradients between shallow and deep piezometers for Khulna and Lakshmipur (3 m and 5 m head difference, respectively, see supporting information) are comparable to downward gradients reported close to Dhaka (2-4.5 m) by Knappett et al (2016). With the exception of site 1 Digha (DI) and…”

“…Regional‐scale modeling (Burgess et al, ; Hoque et al, ; Michael & Voss, , ) and field studies (McArthur et al, ; Mihajlov et al, ; Mukherjee et al, ; Ravenscroft et al, ) have explored the vulnerability of the deep groundwater in the coastal Bengal Aquifer System (BAS) to contamination yet key knowledge gaps remain. These include the relative importance of site‐specific, borehole‐ scale problems due to casing breaks at abstraction well sites (I. Choudhury et al, ) and aquifer‐scale vulnerabilities (Hoque et al, ) to contamination from shallow groundwater and the long‐term impacts of intensive pumping at depth (Khan et al, ; Knappett et al, ; Michael & Khan, ; Zahid et al, ). The presence of modern tracers (e.g., tritium and chlorofluorocarbons (CFCs)) in deeper groundwater systems (typically >150 m) has been attributed to deep pumping in the BAS and in many other aquifer systems globally (Jasechko et al, ; Lapworth et al, ; McMahon et al, ; Samborska et al, ) yet considerable uncertainty remains about the scale and nature of this pumping‐induced contamination.…”

“…These include the relative importance of site-specific, borehole-scale problems due to casing breaks at abstraction well sites (I. Choudhury et al, 2016) and aquifer-scale vulnerabilities (Hoque et al, 2017) to contamination from shallow groundwater and the long-term impacts of intensive pumping at depth Knappett et al, 2016;Zahid et al, 2014). The presence of modern tracers (e.g., tritium and chlorofluorocarbons (CFCs)) in deeper groundwater systems (typically >150 m) has been attributed to deep pumping in the BAS and in many other aquifer systems globally (Jasechko et al, 2017;Lapworth et al, 2015;McMahon et al, 2013;Samborska et al, 2013) yet considerable uncertainty remains about the scale and nature of this pumping-induced contamination.…”

Gestión Del Agua Subterránea De Uso Agrícola: Los Retos De La Sustentabilidad Socio-Ambiental Y La Equidad

“…Los hundimientos de tierra son un fenómeno común en áreas de uso intensivo de aguas subterráneas y conducen a altos costos sociales debido a daños en las tuberías de drenaje, en viviendas y carreteras, y aumento de riesgo de inundaciones. La sobreexplotación también puede tener impactos muy graves sobre la calidad de las aguas subterráneas, como muestran los casos de arsénico en Bangladesh, Bengala occidental (Knappett et al, 2016) y los acuíferos de la Comarca Lagunera y el norte del estado de Guanajuato en México (Knappett et al, 2018). Estas formas de injusticia relacionados con las aguas subterráneas son muy difusas y afectan a amplios segmentos de la población.…”