Megacity pumping and preferential flow threaten groundwater quality.
Many of the world's megacities depend on groundwater from geologically complex aquifers that are over-exploited and threatened by contamination. Here, using the example of Dhaka, Bangladesh, we illustrate how interactions between aquifer heterogeneity and groundwater exploitation jeopardize groundwater resources regionally. Groundwater pumping in Dhaka has caused large-scale drawdown that extends into outlying areas where arsenic-contaminated shallow groundwater is pervasive and has potential to migrate downward. We evaluate the vulnerability of deep, low-arsenic groundwater with groundwater models that incorporate geostatistical simulations of aquifer heterogeneity. Simulations show that preferential flow through stratigraphy typical of fluvio-deltaic aquifers could contaminate deep (>150 m) groundwater within a decade, nearly a century faster than predicted through homogeneous models calibrated to the same data. The most critical fast flowpaths cannot be predicted by simplified models or identified by standard measurements. Such complex vulnerability beyond city limits could become a limiting factor for megacity groundwater supplies in aquifers worldwide.
Department of Geological Sciences, University of Delaware, Newark, Delaware 19716, USA.
Mahfuzur R
http://orcid.org/0000-0003-2960-9648
MR
Khan
Department of Geological Sciences, University of Delaware, Newark, Delaware 19716, USA.
Mohammad
M
Koneshloo
Geology and Geophysics, Texas A&M University, College Station, Texas 77843, USA.
Peter S K
PS
Knappett
Department of Geology, University of Dhaka, Dhaka 1000, Bangladesh.
Kazi M
KM
Ahmed
Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA.
Benjamin C
BC
Bostick
Environmental Sciences, Barnard College, New York, New York 10027, USA.
Brian J
BJ
Mailloux
Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA.
Rajib H
RH
Mozumder
Department of Geology, University of Dhaka, Dhaka 1000, Bangladesh.|Bangladesh Water Development Board, Government of Bangladesh, Green Road, Dhaka 1000, Bangladesh.
Anwar
A
Zahid
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge Massachussetts, 02197, USA.
Charles F
CF
Harvey
Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA.
Alexander
A
van Geen
Department of Geological Sciences, University of Delaware, Newark, Delaware 19716, USA.|Department of Civil and Environmental Engineering, University of Delaware, Newark, Delaware 19716, USA.
Holly A
HA
Michael
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