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TitleArsenic release and geochemical evolution of groundwater in an alluvial aquitard, West Bengal, India
AuthorDesbarats, A JORCID logo; Pal, T; Mukherjee, P K; Beckie, R D
Source2017 American Geophysical Union Fall Meeting, Fall Meeting supplement; Eos, Transactions of the American Geophysical Union vol. 98, no. 52, H13J-1852, 2017 p. 1 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesNatural Resources Canada, Contribution Series 20190247
PublisherAmerican Geophysical Union
Meeting2017 American Geophysical Union Fall Meeting; New Orleans, LA; US; December 11-15, 2017
Mediaon-line; digital
File formathtml; pdf
AreaWest Bengal; India
Lat/Long WENS 88.3167 88.9667 23.2833 22.8000
Subjectshydrogeology; surficial geology/geomorphology; environmental geology; geochemistry; mineralogy; Nature and Environment; Science and Technology; Health and Safety; arsenic; arsenic geochemistry; aquifers; organic carbon; groundwater geochemistry; groundwater flow; groundwater pollution; minerals; chlorite; goethite; vivianite; precipitation; organic carbon; models; sediment geochemistry; weathering; phosphorus geochemistry; phyllosilicates; alluvial sediments; Health hazards; Environmental hazards
ProgramEnvironmental Geoscience Tools for environmental impacts and adaptation for metal mining
Released2017 12 01
AbstractAccording to the World Health Organization, contamination of groundwater by geogenic arsenic (As) represents the largest mass poisoning in history. At a field site in West Bengal, India, the source of As affecting a shallow aquifer was traced to silty sediments filling an abandoned river meander. Along with As-bearing phases, these sediments also contain 0.46 % organic carbon. The release of As within the channel fill is investigated using a geochemical mass balance model supported by detailed field observations of aqueous chemistry, sequential extraction analyses of sediment chemistry, and analyses of sediment mineralogy. The model explores the evolution of groundwater chemistry along a flow path extending from its recharge point in an abandoned channel pond, through the channel-fill sequence, to the underlying aquifer. Variations in groundwater composition within the host sediments are explained in terms of mineral weathering driven by organic carbon decay. The model yields reaction coefficients expressing amounts of minerals (and gases) reacting or precipitating along the flow path. Arsenic and phosphorus cycles appear closely linked as these species are hosted by goethite, Fe-rich chlorite, and vivianite. Arsenic is released through the rapid reductive dissolution of goethite and the slower weathering of chlorite. Concomitantly, some As is sequestered in precipitating vivianite. These competing processes reach equilibrium deeper in the channel-fill sequence as groundwater As concentrations stabilize. Using groundwater residence time in channel fill obtained from a numerical flow model and the calculated reaction coefficients, rates of organic carbon oxidation, goethite dissolution, and net As release are estimated at 1.15 mmol C L-1 a-1, 0.18 mmol L-1 a-1, and 4.57 10-4 mmol L-1 a-1, respectively. Fine-grained yet slightly permeable deposits such as channel-fill silts containing reactive organic carbon and As-bearing goethite and phyllosilicates are localized centers of intense chemical weathering conducive to As mobilization.
Summary(Plain Language Summary, not published)
Groundwater contamination by geogenic arsenic is impacting the health of over 100 million people across Asia. According to the World Health Organisation, this is the largest mass poisoning in history. To advance understanding of the arsenic source and fundamental processes involved in its release, scientists from the Geological Surveys of Canada and India, and the University of British Columbia, undertook a joint research project in an affected village of West Bengal. This paper describes the geochemical evolution of groundwater as it flows through arsenic source sediments deposited in an abandoned river meander. A mass balance model was developed to explain groundwater composition and arsenic release in terms of the dissolution or precipitation of minerals found in the sediments. This study has yielded new knowledge of arsenic hosts and release processes, and it represents an important step toward the development of sound public health mitigation schemes in India and elsewhere.

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