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Arsenic Geochemistry in the Alluvial Aquifers of West Bengal, India: Implications for targeting safe aquifers for sustainable drinking water supply
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. (KTH-Groundwater Arsenic Research Group)
2013 (Estonian)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The natural occurrences of high (>10 μg/L) dissolved arsenic (As) in groundwater of Bengal Basin has put millions of people under the threat of chronic As exposure through drinking water. Present study has examined the processes that regulate As mobilization and its distribution in shallow aquifers and the potentiality of finding safe aquifers within shallow depth (<50 m) for drinking water supply. The results indicate that in terms of aquifer sediment colors and water quality two types of aquifer namely brown sand aquifer (BSA) and grey sand aquifer (GSA) can be distinguished within the depth, accessible by low-cost drilling. The redox condition in the BSA is delineated to be Mn oxyhydroxides reducing, not sufficiently lowered for As mobilization resulting in high Mn and low Fe and As in groundwater. While in GSA, currently the reductive dissolution of Fe oxyhydroxides is the prevailing redox process causing As mobilization into groundwater of this aquifer type. It is revealed that the vertical distribution of As and other aqueous redox parameters is related to the redox zonation within aquifer. The decoupling of As and Fe release into groundwater is evident in the shallowest part of aquifer because of Fe enrichment by weathering of silicate minerals especially of biotite, the precipitation of secondary mineral phases like siderite and vivianite and incomplete reduction of Fe oxyhydroxides. It is characterized that the seasonal variations of As and other aqueous solutes are limited within the upper portion of aquifer only (<30 m bgl) and can be related to seasonal cycling of redox status, aggregation and dispersion of As scavenging colloids, local groundwater abstraction and monsoonal recharge. The results of surface complexation modeling indicate that PO43- is the major competitor of As(III) and As(V) adsorption onto Fe oxyhydroxides. This study concludes that the reductive dissolution of Fe oxyhydroxides followed by competitive sorption reactions with the aquifer sediment is the process conducive for As enrichment in groundwater of Bengal Basin. Present study advocates that despite low concentration of As in groundwater, a rigorous assessment of attendant health risk for Mn is necessary prior to considering mass scale exploitation of the BSA for sustainable drinking water supply. This study also validates that TW platform colors can be used as a rapid screening tool for As and Mn in drinking water wells to prioritize As mitigation management.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , xii, 71 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1071
Keyword [en]
Bengal Basin; Groundwater; Arsenic; Redox processes; Competing ions; Sustainable drinking water Supply
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-128938ISBN: 978-91-7501-849-2 (print)OAI: oai:DiVA.org:kth-128938DiVA: diva2:648944
Public defence
2013-09-23, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
EURINDIA 2009-1665
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research, 2005-035-137
Note

QC 20130919

Available from: 2013-09-19 Created: 2013-09-17 Last updated: 2013-09-27Bibliographically approved
List of papers
1. Hydrogeochemical contrast between brown and grey sand aquifers in shallow depth of Bengal Basin: Consequences for sustainable drinking water supply
Open this publication in new window or tab >>Hydrogeochemical contrast between brown and grey sand aquifers in shallow depth of Bengal Basin: Consequences for sustainable drinking water supply
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2012 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 431, 402-412 p.Article in journal (Refereed) Published
Abstract [en]

Delineation of safe aquifer(s) that can be targeted by cheap drilling technology for tubewell (TW) installation becomes highly imperative to ensure access to safe and sustainable drinking water sources for the arsenic (As) affected population in Bengal Basin. This study investigates the potentiality of brown sand aquifers (BSA) as a safe drinking water source by characterizing its hydrogeochemical contrast to grey sand aquifers (GSA) within shallow depth (<70 m) over an area of 100 km(2) in Chakdaha Block of Nadia district, West Bengal, India. The results indicate that despite close similarity in major ion composition, the redox condition is markedly different in groundwater of the two studied aquifers. The redox condition in the BSA is delineated to be Mn oxy-hydroxide reducing, not sufficiently lowered for As mobilization into groundwater. In contrast, the enrichments of NH4+, PO43-, Fe and As along with lower Eh in groundwater of GSA reflect reductive dis-solution of Fe oxy-hydroxide coupled to microbially mediated oxidation of organic matter as the prevailing redox process causing As mobilization into groundwater of this aquifer type. In some portions of GSA the redox status even has reached to the stage of SO42- reduction, which to some extent might sequester dissolved As from groundwater by co-precipitation with authigenic pyrite. Despite having low concentration of As in groundwater of the BSA the concentration of Mn often exceeds the drinking water guidelines, which warrants rigorous assessment of attendant health risk for Mn prior to considering mass scale exploitation of the BSA for possible sustainable drinking water supply.

Keyword
Bengal Basin, Arsenic, Manganese, Redox condition, Sustainable drinking water supply
National Category
Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-102351 (URN)10.1016/j.scitotenv.2012.05.031 (DOI)000306887900048 ()2-s2.0-84862158832 (Scopus ID)
Funder
Swedish Research Council, 348-2006-6005
Note

QC 20120914

Available from: 2012-09-14 Created: 2012-09-14 Last updated: 2017-12-07Bibliographically approved
2. Testing tubewell platform color as a rapid screening tool for arsenic and manganese in drinking water wells
Open this publication in new window or tab >>Testing tubewell platform color as a rapid screening tool for arsenic and manganese in drinking water wells
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2012 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, ISSN 0013-936X, Vol. 46, 434-440 p.Article in journal (Refereed) Published
Abstract [en]

A low-cost rapid screening tool for arsenic (As) and manganese (Mn) in groundwater is urgently needed to formulate mitigation policies for sustainable drinking water supply. This study attempts to make statistical comparison between tubewell (TW)platform color and the level of As and Mn concentration in groundwater extracted from the respective TW (n = 423), to validate platform color as a screening tool for As andMnin groundwater. The result shows that a black colored platform with 73% certainty indicates that well water is safe fromAs, while with 84% certainty a red colored platform indicates that well water is enriched with As, compared to WHO drinking waterguideline of 10 μg/L. With this guideline the efficiency, sensitivity, and specificity of the tool are 79%, 77%, and 81%, respectively.However, the certainty values become 93% and 38%, respectively, for black and redcolored platforms at 50 μg/L, the drinking water standards for India and Bangladesh. The respective efficiency, sensitivity, and specificity are 65%, 85%, and 59%. Similarly for Mn, black and red colored platform with 78% and 64% certainty, respectively, indicates that wellwater is either enriched or free from Mn at the Indian national drinking water standard of 300 μg/L. With this guideline the efficiency, sensitivity, and specificity of the tool are 71%, 67%, and 76%, respectively. Thus, this study demonstrates that TWplatform color can bepotentially used as an initial screening tool for identifying TWs with elevated dissolved As andMn, tomake further rigorous groundwater testing more intensive and implement mitigation options for safe drinking water supplies.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-85973 (URN)10.1021/es203058a (DOI)000298762900058 ()2-s2.0-84855321319 (Scopus ID)
Projects
VR-Sida, Mistra, EURINDIA
Funder
Swedish Research Council, 348-2006-6005
Note
QC 20120227Available from: 2012-02-13 Created: 2012-02-13 Last updated: 2017-12-07Bibliographically approved

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