tailieunhanh - NATURAL ARSENIC IN GROUNDWATER: OCCURRENCE, REMEDIATION AND MANAGEMENT - CHAPTER 16

Nước ngầm làm giàu asen geogenic là thường gặp phải trong các tầng chứa nước trầm tích Holocene của đồng bằng đồng bằng sông Bengal (BDP). | Section 3 Arsenic biogeochemistry in groundwater Copyright 2005 Taylor Francis Group plc London UK Natural Arsenic in Groundwater Occurrence Remediation and Management -Bundschuh Bhattacharya and Chandrasekharam eds 2005 Taylor Francis Group London ISBN 04 1536 700 X Natural enrichment of arsenic in groundwaters of Brahmanbaria district Bangladesh geochemistry speciation modeling and multivariate statistics Ondra Sracek Institute of Geological Sciences Faculty of Science Masaryk University Brno Czech Republic Prosun Bhattacharya Mattias von Bromssen Gunnar Jacks Groundwater Arsenic Research Group Department of Land and Water Resources Engineering Royal Institute ofTechnology KTH Stockholm Sweden Kazi Matin Ahmed Department of Geology University of Dhaka Dhaka Bangladesh ABSTRACT Groundwater with geogenic arsenic enrichment is commonly encountered in the Holocene sedimentary aquifers of the Bengal Delta Plain BDP . The present study was carried out in Brahmanbaria district covering an area of18 km2 in northeastern Bangladesh. The Chandina Formation is the main hydrostratigraphic unit of the area which comprises silt and clay with high content of organic matter. Dissolved arsenic concentrations in groundwater are high reaching 400 g L in some wells. Groundwater is reducing with general lack of detectable dissolved oxygen DO and contains low concentrations of nitrate and sulfate. Concentrations of dissolved Fe are high which is in general in agreement with the reductive dissolution of ferric oxide and hydroxide hypothesis. Results of speciation modeling indicated the possibility of precipitation of siderite and to less extent vivianite for many samples. The log PCO2 values were extremely high atm suggesting production of CO2 in redox reactions involving the organic matter in the sediments. Redox potential values calculated on the basis of different redox couples and field Eh measurement indicated redox disequilibrium. Hierarchical cluster analysis HCA performed in