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TitleGroundwater flow dynamics and arsenic source characterization in an aquifer system of West Bengal, India
AuthorDesbarats, A JORCID logo; Koenig, C E M; Pal, T; Mukherjee, P K; Beckie, R D
SourceWater Resources Research vol. 50, no. 6, 2014 p. 4974-5002,
Alt SeriesEarth Sciences Sector, Contribution Series 20120463
Mediapaper; on-line; digital
File formatpdf
AreaWest Bengal; India
Lat/Long WENS 88.3167 88.9667 23.2833 22.8000
Subjectshydrogeology; environmental geology; groundwater; groundwater circulation; groundwater flow; groundwater regimes; arsenic; heavy metals contamination; aquifers
Illustrationslocation maps; photographs; histograms; tables; stratigraphic columns
ProgramEnvironmental Geoscience, Management
Released2014 06 18
AbstractNumerical groundwater flow modeling, reverse particle tracking, and environmental tracers are used to locate the source of geogenic As affecting an aquifer in West Bengal. The aquifer is hosted by point-bar sands deposited in a meandering fluvial environment. Wells tapping the aquifer exhibit As concentrations up to 531 ?g/L. High-As groundwaters are recharged in ponds marking an abandoned river channel. The source of As is traced to the underlying fine-grained channel-fill sediments. Arsenic release within these sediments is accompanied by a concomitant release of Br and DOC indicating that these species may be decay products of natural organobromines codeposited along with As. Mass transfer of As to the dissolved phase and its flushing from source sediments are described using a simplified reactive solute transport model. Based on this model, a characteristic reaction time for mass transfer is estimated at 6.7 years. Average groundwater residence times in the source are estimated to have declined from 16.6 to 6.6 years with the advent of intensive irrigation pumping. The ratio of residence and reaction times, a Damköhler number, has declined correspondingly from 2.49 to 0.99, indicating a shift from transport to reaction rate limited As mobilization. Greater insight into the As problem in SE Asia may be achieved by shifting the focus of field investigations from aquifers to potential contamination sources in aquitards.
Summary(Plain Language Summary, not published)
Groundwater contamination by arsenic from natural sources is affecting the health of over 100 million people throughout Asia and this is the largest mass poisoning in history according to the World Health Organisation. To further understanding on the source of arsenic and on the processes involved in its release, the Geological Surveys of Canada and of India, and the University of British Columbia, undertook a joint research project in an affected village of West Bengal. This paper describes the combined use of computational groundwater flow modeling and geochemical pathfinders to trace the source of arsenic in well water and to estimate the rate at which it is being released. Sediments deposited in abandoned river channels are found to be the source of both the arsenic and the organic matter that fuels its release. This new understanding of the nature of arsenic source sediments is a prerequisite to the development of sound public health mitigation schemes in India and elsewhere.

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