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Mozumder MRH, Michael HA, Mihajlov I, Khan MR, Knappett PSK, Bostick BC, Mailloux BJ, Ahmed KM, Choudhury I, Koffman T, Ellis T, Whaley-Martin K, San Pedro R, Slater G, Stute M, Schlosser P, van Geen A. Origin of Groundwater Arsenic in a Rural Pleistocene Aquifer in Bangladesh Depressurized by Distal Municipal Pumping. Water Resour Res 2020; 56:e2020WR027178. [PMID: 33958831 PMCID: PMC8099038 DOI: 10.1029/2020wr027178] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2020] [Accepted: 04/30/2020] [Indexed: 05/26/2023]
Abstract
Across South Asia, millions of villagers have reduced their exposure to high-arsenic (As) groundwater by switching to low-As wells. Isotopic tracers and flow modeling are used in this study to understand the groundwater flow system of a semi-confined aquifer of Pleistocene (>10 kyr) age in Bangladesh that is generally low in As but has been perturbed by massive pumping at a distance of about 25 km for the municipal water supply of Dhaka. A 10- to 15-m-thick clay aquitard caps much of the intermediate aquifer (>40- to 90-m depth) in the 3-km2 study area, with some interruptions by younger channel sand deposits indicative of river scouring. Hydraulic heads in the intermediate aquifer below the clay-capped areas are 1-2 m lower than in the high-As shallow aquifer above the clay layer. In contrast, similar heads in the shallow and intermediate aquifer are observed where the clay layer is missing. The head distribution suggests a pattern of downward flow through interruptions in the aquitard and lateral advection from the sandy areas to the confined portion of the aquifer. The interpreted flow system is consistent with 3H-3He ages, stable isotope data, and groundwater flow modeling. Lateral flow could explain an association of elevated As with high methane concentrations within layers of gray sand below certain clay-capped portions of the Pleistocene aquifer. An influx of dissolved organic carbon from the clay layer itself leading to a reduction of initially orange sands has also likely contributed to the rise of As.
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Affiliation(s)
- M. R. H. Mozumder
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
- Now at Gradient, Boston, MA, USA
| | - H. A. Michael
- Department of Earth Sciences, University of Delaware, Newark, DE, USA
| | - I. Mihajlov
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
- Now at Geosyntec Consultants, Huntington Beach, CA, USA
| | - M. R. Khan
- Department of Geology, University of Dhaka, Dhaka, Bangladesh
| | - P. S. K. Knappett
- Geology & Geophysics, Texas A&M University, College Station, TX, USA
| | - B. C. Bostick
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
| | - B. J. Mailloux
- Environmental Science, Barnard College, New York, NY, USA
| | - K. M. Ahmed
- Department of Geology, University of Dhaka, Dhaka, Bangladesh
| | - I. Choudhury
- Department of Geology, University of Dhaka, Dhaka, Bangladesh
| | - T. Koffman
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
- Now at Land Resources and Environmental Sciences, Montana State University, Bozeman, MT, USA
| | - T. Ellis
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
| | - K. Whaley-Martin
- Earth and Environmental Sciences, McMaster University, Hamilton, Ontario, Canada
- Now at Civil and Mineral Engineering Department, University of Toronto, Ontario, Canada
| | - R. San Pedro
- Earth and Environmental Sciences, McMaster University, Hamilton, Ontario, Canada
| | - G. Slater
- Earth and Environmental Sciences, McMaster University, Hamilton, Ontario, Canada
| | - M. Stute
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
- Environmental Science, Barnard College, New York, NY, USA
| | - P. Schlosser
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
- Now at Julie Ann Wrigley Global Institute of Sustainability, Arizona State University, Tempe, AZ, USA
| | - A. van Geen
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
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Knappett PSK, Mailloux BJ, Choudhury I, Khan MR, Michael HA, Barua S, Mondal DR, Steckler MS, Akhter SH, Ahmed KM, Bostick B, Harvey CF, Shamsudduha M, Shuai P, Mihajlov I, Mozumder R, van Geen A. VULNERABILITY OF LOW-ARSENIC AQUIFERS TO MUNICIPAL PUMPING IN BANGLADESH. J Hydrol (Amst) 2016; 539:674-686. [PMID: 28966395 PMCID: PMC5617134 DOI: 10.1016/j.jhydrol.2016.05.035] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
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.
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Affiliation(s)
- P. S. K. Knappett
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
- Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843
| | - B. J. Mailloux
- Department of Environmental Science, Barnard College, New York, NY 10027
| | - I. Choudhury
- Department of Geology, University of Dhaka, Dhaka 1000, Bangladesh
| | - M. R. Khan
- Department of Geological Sciences, University of Delaware, Newark, DE 19716
| | - H. A. Michael
- Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716
| | - S. Barua
- Department of Geology, Kansas State University, Manhattan, KS 66506
| | - D. R. Mondal
- School of Earth & Environmental Sciences, Queens College, Queens, NY 11367
| | - M. S. Steckler
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
| | - S. H. Akhter
- Department of Geology, University of Dhaka, Dhaka 1000, Bangladesh
| | - K. M. Ahmed
- Department of Geology, University of Dhaka, Dhaka 1000, Bangladesh
| | - B. Bostick
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
| | - C. F. Harvey
- Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - M. Shamsudduha
- Institute for Risk & Disaster Reduction, University College London, London WC1E 6BT, UK
| | - P. Shuai
- Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843
| | - I. Mihajlov
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
| | - R. Mozumder
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
| | - A. van Geen
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
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Radloff KA, Zheng Y, Michael HA, Stute M, Bostick BC, Mihajlov I, Bounds M, Huq MR, Choudhury I, Rahman MW, Schlosser P, Ahmed KM, van Geen A. Arsenic migration to deep groundwater in Bangladesh influenced by adsorption and water demand. Nat Geosci 2011; 4:793-798. [PMID: 22308168 PMCID: PMC3269239 DOI: 10.1038/ngeo1283] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Drinking shallow groundwater with naturally elevated concentrations of arsenic is causing widespread disease in many parts of South and Southeast Asia. In the Bengal Basin, growing reliance on deep (>150 m) groundwater has lowered exposure. In the most affected districts of Bangladesh, shallow groundwater concentrations average 100 to 370 μg L(-1), while deep groundwater is typically < 10 μg L(-1). Groundwater flow simulations have suggested that, even when deep pumping is restricted to domestic use, deep groundwater in some areas of the Bengal Basin is at risk of contamination. However, these simulations have neglected the impedance of As migration by adsorption to aquifer sediments. Here we quantify for the first time As sorption on deeper sediments in situ by replicating the intrusion of shallow groundwater through injection of 1,000 L of deep groundwater modified with 200 μg L(-1) of As into a deeper aquifer. Arsenic concentrations in the injected water were reduced by 70% due to adsorption within a single day. Basin-scale modelling indicates that while As adsorption extends the sustainable use of deep groundwater, some areas remain vulnerable; these areas can be prioritized for management and monitoring.
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