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Hydrogeological and geochemical assessment of aquifer systems with geogenic arsenic in Southeastern Bangladesh: Targeting low arsenic aquifers for safe drinking water supplies in Matlab
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology. (KTH-International Groundwater Arsenic Research Group)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Naturally occurring arsenic (As) in Holocene aquifers in Bangladesh have undermined a long success of supplying the population with safe drinking water. Arsenic is mobilised in reducing environments through reductive dissolution of Fe(III)-oxyhydroxides. Several studies have shown that many of the tested mitigation options have not been well accepted by the people. Instead, local drillers target presumed safe groundwater on the basis of the colour of the sediments. The overall objective of the study has thus been focussed on assessing the potential for local drillers to target As safe groundwater. The specific objectives have been to validate the correlation between aquifer sediment colours and groundwater chemical composition, characterize aqueous and solid phase geochemistry and dynamics of As mobility and to assess the risk for cross-contamination of As between aquifers in Daudkandi and Matlab Upazilas in SE-Bangladesh. In Matlab, drillings to a depth of 60 m revealed two distinct hydrostratigraphic units, a strongly reducing aquifer unit with black to grey sediments overlies a patchy sequence of weathered and oxidised white, yellowish-grey to reddish-brown sediment. The aquifers are separated by an impervious clay unit. The reducing aquifer is characterized by high concentrations of dissolved As, DOC, Fe and PO43--tot. On the other hand, the off-white and red sediments contain relatively higher concentrations of Mn and SO42- and low As. Groundwater chemistry correlates well with the colours of the aquifer sediments. Geochemical investigations indicate that secondary mineral phases control dissolved concentrations of Mn, Fe and PO43--tot. Dissolved As is influenced by the amount of Hfo, pH and PO43--tot as a competing ion. Laboratory studies suggest that oxidised sediments have a higher capacity to absorb As. Monitored hydraulic heads and groundwater modelling illustrate a complex aquifer system with three aquifers to a depth of 250 m. Groundwater modelling illustrate two groundwater flowsystems: i) a deeper regional predominantly horizontal flow system, and ii) a number of shallow local flow systems. It was confirmed that groundwater irrigation, locally, affects the hydraulic heads at deeper depths. The aquifer system is however fully recharged during the monsoon. Groundwater abstraction for drinking water purposes in rural areas poses little threat for cross-contamination. Installing irrigation- or high capacity drinking water supply wells at deeper depths is however strongly discouraged and assessing sustainability of targeted low-As aquifers remain a main concern. The knowledge gained here can be used for developing guidelines for installing safe wells at similar environments in other areas of Bangladesh.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xii, 46 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1063
Keyword [en]
Arsenic, Bangladesh, drinking water, groundwater, sustainability, geochemistry, hydrogeology, modelling
National Category
Oceanography, Hydrology, Water Resources Geochemistry Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-53300ISBN: 978-91-7501-214-8 (print)OAI: oai:DiVA.org:kth-53300DiVA: diva2:469798
Public defence
2012-01-20, F3, Lindstedtsvägen 26, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20111227Available from: 2011-12-27 Created: 2011-12-27 Last updated: 2011-12-27Bibliographically approved
List of papers
1. Targeting low-arsenic aquifers in Matlab Upazila, Southeastern Bangladesh
Open this publication in new window or tab >>Targeting low-arsenic aquifers in Matlab Upazila, Southeastern Bangladesh
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2007 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 375, no 2-3, 121-132 p.Article in journal (Refereed) Published
Abstract [en]

Groundwater with high concentration of geogenic arsenic (As) occurs extensively in the Holocene alluvial aquifers of Bangladesh. Local drillers in Matlab Upazilla are constructing deeper tubewells than in the recent past, primarily because of low concentrations of dissolved Fe and As. Locally a thick layer of black to grey sediments overlies an oxidised unit of yellowish-grey to reddish-brown sediments. The correlation between the colour of both units and the groundwater redox conditions was investigated to provide an easy tool for targeting low-arsenic groundwater. Based on the sediment colour at the screen depths described by local drillers, 40 domestic shallow tubewells were selected for water sampling. Four colours were used to describe the sediments: black, white, off-white (buff) and red. Generally, the groundwater was anoxic and the As concentrations ranged from less than 5.2 to 355 mu g/L. Water derived from the black sediment is characterized by relatively higher concentrations of dissolved NH4+, DOC, Fe, P, As and by low Mn and SO42- concentrations. The off-white and red sediments had high concentration of Mn and low NH4+, DOC, Fe, P and As concentrations. The water abstracted from the black sediments indicated the most reducing environment, followed by white, off-white and red respectively. Three boreholes verified the driller's perception of the subsurface lithologic conditions. Discrepancies between the driller's and the research team description of the sediment colours were insignificant. This study shows that sediment colour is a reliable indicator of high and low-As concentrations and can be used by local drillers to target low-arsenic groundwater.

Keyword
Bangladesh; Geogenic arsenic; Groundwater; Local drillers; Sediment colour; Targeting safe aquifers
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:kth:diva-7089 (URN)10.1016/j.scitotenv.2006.06.028 (DOI)000247354700002 ()17113133 (PubMedID)2-s2.0-34249057119 (Scopus ID)
Note
QC 20100716. Uppdaterad från In press till Published 20100716. Tidigare titel: "Targeting low-arsenic aquifers in Matlab upazila, Southeastern Bangladesh: Science of the Total Environment"Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2011-12-27Bibliographically approved
2. Geochemical characterisation of shallow aquifer sediments of Matlab Upazila, Southeastern Bangladesh - Implications for targeting low-As aquifers
Open this publication in new window or tab >>Geochemical characterisation of shallow aquifer sediments of Matlab Upazila, Southeastern Bangladesh - Implications for targeting low-As aquifers
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2008 (English)In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 99, no 1-4, 137-149 p.Article in journal (Refereed) Published
Abstract [en]

High arsenic (As) concentrations in groundwater pose a serious threat to the health of millions of people in Bangladesh. Reductive dissolution of Fe(Ill)-oxyhydroxides and release of its adsorbed As is considered to be the principal mechanism responsible for mobilisation ofAs. The distribution ofAs is extremely heterogeneous both laterally and vertically. Groundwater abstracted from oxidised reddish sediments, in contrast to greyish reducing sediments, contains significantly lower amount of dissolved arsenic and can be a source of safe water. In order to study the sustainability of that mitigation option, this study describes the lithofacies and genesis of the sediments within 60 m depth and establishes a relationship between aqueous and solid phase geochemistry. Oxalate extractable Fe and Mn contents are higher in the reduced unit than in the oxidised unit, where Fe and Mn are present in more crystalline mineral phases. Equilibrium modelling of saturation indices suggest that the concentrations of dissolved Fe, Mn and PO43--tot in groundwater is influenced by 4 secondary mineral phases in addition to redox processes. Simulating As-[I] adsorption on hydroferric oxides using the Diffuse Layer Model and analytical data gave realistic concentrations of dissolved and adsorbed As-[I] for the reducing aquifer and we speculate that the presence of high PO43--tot in combination with reductive dissolution results in the high-As groundwater. The study confirms high mobility of As in reducing aquifers with typically dark colour of sediments found in previous studies and thus validates the approach for location of wells used by local drillers based on sediment colour. A more systematic and standardised colour description and similar studies at more locations are necessary for wider application of the approach.

Keyword
arsenic, groundwater, Bangladesh, redox, hydrogeochemistry, shallow, sedimentary aquifer, arsenic enrichment, west-bengal, reducing conditions, alluvial, aquifers, groundwater, extraction, mobility, delta, environments, mitigation
National Category
Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-17811 (URN)10.1016/j.jconhyd.2008.05.005 (DOI)000259055100010 ()2-s2.0-48549085236 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Geochemistry and mineralogy of shallow alluvial aquifers in Daudkandi upazila in the Meghna flood plain, Bangladesh
Open this publication in new window or tab >>Geochemistry and mineralogy of shallow alluvial aquifers in Daudkandi upazila in the Meghna flood plain, Bangladesh
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2009 (English)In: Environmental Geology, ISSN 0943-0105, E-ISSN 1432-0495, Vol. 57, no 3, 499-511 p.Article in journal (Refereed) Published
Abstract [en]

The shallow alluvial aquifers of the delta plains and flood plains of Bangladesh, comprises about 70% of total land area are mostly affected by elevated concentrations of arsenic (As) in groundwater exposing a population of more than 35 million to As toxicity. Geochemical studies of shallow alluvial aquifer in the Meghna flood plain show that the uppermost yellowish grey sediment is low in As (1.03 mg/kg) compared to the lower dark grey to black sediment (5.24 mg/kg) rich in mica and organic matter. Sequential extraction data show that solid phase As bound to poorly crystalline and amorphous metal (Fe, Mn, Al)-oxyhydroxides is dominant in the grey to dark grey sediment and reaches its maximum level (3.05 mg/kg) in the mica rich layers. Amount of As bound to sulphides and organic matter also peaks in the dark grey to black sediment. Vertical distributions of major elements determined by X-ray fluorescence (XRF) show that iron (Fe2O3), aluminum (Al2O3) and manganese (MnO) follow the general trend of distribution of As in the sediments. Concentrations of As, Mn, Fe, HCO3 (-), SO4 (2-) and NO3 (-) in groundwater reflect the redox status of the aquifer and are consistent with solid phase geochemistry. Mineralogical analysis by X-ray diffraction (XRD) and scanning electron microscopy (SEM) fitted with energy dispersive X-ray spectrometer (EDS) revealed dominance of crystalline iron oxides and hydroxides like magnetite, hematite and goethite in the oxidised yellowish grey sediment. Amorphous Fe-oxyhydroxides identified as grain coating in the mica and organic matter rich sediment suggests weathering of biotite is playing a critical role as the source of Fe(III)-oxyhydroxides which in turn act as sink for As. Presence of authigenic pyrite in the dark grey sediment indicates active reduction in the aquifer.

Keyword
Alluvial aquifer; Bangladesh; Redox status; Metal-oxyhydroxides; Arsenic mobility
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-9346 (URN)10.1007/s00254-008-1319-8 (DOI)000263870000002 ()2-s2.0-67349084419 (Scopus ID)
Note
QC 20100809. Uppdaterad från in press till published (20100809).Available from: 2008-10-21 Created: 2008-10-21 Last updated: 2011-12-27Bibliographically approved
4. Dynamics of arsenic adsorption in the targeted arsenic-safe aquifers in Mat lab, south-eastern Bangladesh: Insight from experimental studies
Open this publication in new window or tab >>Dynamics of arsenic adsorption in the targeted arsenic-safe aquifers in Mat lab, south-eastern Bangladesh: Insight from experimental studies
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2011 (English)In: Journal of Applied Geochemistry, ISSN 0883-2927, Vol. 26, no 4, 624-635 p.Article in journal (Refereed) Published
National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-33256 (URN)10.1016/j.apgeochem.2011.01.019 (DOI)000289384200019 ()2-s2.0-79952619004 (Scopus ID)
Note
QC 20110503Available from: 2011-05-03 Created: 2011-05-02 Last updated: 2012-03-22Bibliographically approved
5. Hydrogeochemical evaluation of groundwater along an E-W transect in the Meghna basin, Bangladesh
Open this publication in new window or tab >>Hydrogeochemical evaluation of groundwater along an E-W transect in the Meghna basin, Bangladesh
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(English)Manuscript (Other academic)
Keyword
groundwater composition, transect, lithofacies, Meghna basin, Bangladesh
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-9347 (URN)
Note
QC 20100809Available from: 2008-10-21 Created: 2008-10-21 Last updated: 2011-12-27Bibliographically approved

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