2006 Fiscal Year Final Research Report Summary
Clarify on the formation mechanism of arsenic contaminated groundwater in the alluvial plain of Bangladesh
| Project/Area Number |
15403017
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 海外学術 |
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| Research Field |
Geochemistry/Astrochemistry
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| Research Institution | Osaka City University |
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Principal Investigator |
MITAMURA Muneki Osaka City University, Graduate School of Science, Assosiate Professor, 大学院理学研究科, 助教授 (00183632)
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| Co-Investigator(Kenkyū-buntansha) |
MASUDA Harue (中屋 晴恵) Osaka City University, Graduate School of Science, Assosiate Professor, 大学院理学研究科, 助教授 (70183944)
AKAI Junji Niigata University, Faculty of Science, Professor, 理学部, 教授 (30101059)
CHIBA Hitoshi Okayama University, Faculty of Science, Professor, 理学部, 教授 (30144736)
NAKAYA Shinji Shinshu University, Faculty of Science, Assosiate Professor, 工学部, 助教授 (70313830)
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| Project Period (FY) |
2003 – 2006
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| Keywords | Bangladesh / arsenic / groundwater / alluvial plain / aquifer / Holocene / oxidizing-reducing / delta |
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| Research Abstract |
Continuous sediment core samples and groundwaters were collected in the northern part of Sonargaon, Narayanganj, Bangladesh in the Ganges-Brahmaputra Delta in order to figure out the geological structure of the As-contaminated groundwater aquifers. The study area spans the alluvial plain and the Pleistocene terrace. The Quaternary strata in this area are divided into the Plio-Pleistocene sand, Upper Pleistocene mud, and Holocene sand units in the ascending order. The upper surface of the Upper Pleistocene mud unit are partly eroded and formed depression or valley where the Holocene sand unit is thicker than the surroundings and As-contamination is very high. The uppermost part of the lower aquifer in the Pleistocene terrace deposits was laterized reddish sediments, bordering the overlying impermeable mud unit. The groundwater in this aquifer preserves the oxidizing conditions with almost arsenic free nature. Highly As-contaminated groundwater is found in the upper aquifer in the Holocene sand unit filling in the alluvial plain. Highly As contaminated groundwater appears closely related to the silt to fine sand lenses, and As free groundwater can be obtained from where only sandy sediments comprising coarser than medium sand fraction were recovered in the sediment column. Such a limited occurrence of highly As contaminated groundwater suggests that the contamination occurs during vertical infiltration of groundwater through silt to fine sand lens along or around the installed well tubes due to excess use of the groundwater.
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