Effect of hydrological flow pattern on groundwater arsenic concentration in Bangladesh by Khandaker Ashfaque.

Widespread arsenic contamination of groundwater has become a major concern in Bangladesh since the water supply, particularly in rural areas, is heavily dependent on groundwater. However, relative to the extent of research on biogeochemical processes of arsenic mobilization, very little work has been conducted to understand the complex transient dynamics of groundwater flow, and the transport of arsenic and other solutes that control its mobility in the area. A detailed three-dimensional hydrological model of our study area in Munshiganj indicates that: (1) the shallow aquifer acts primarily as a conduit for flow from ponds and rice fields to irrigation wells and rivers; (2) most inflow to the aquifer occurs during the dry season, and monsoon contributes relatively little to the inflow since the aquifer storage is small; (3) since the increase in irrigation pumping and pond construction have changed the groundwater flow dynamics, arsenic concentrations are unlikely to be at steady-state. These observations are consistent with those from the lumped-parameter model. Analysis of various fluxes from the three-dimensional groundwater model also reveals that ponds provide the largest source of recharge to the aquifer, and hence, is a potential source of dissolved arsenic to the subsurface. Accordingly, a "Pond Hypothesis" has been developed suggesting that arsenic mobilization in Bangladesh aquifer is deriving from reductive dissolution of various arsenic bearing oxides (the widely accepted mechanism for arsenic mobilization in Bangladesh) deposited at the pond bottoms. The process of reductive dissolution occurs in the presence of organic matter and under reducing environment, when residing microbes respire on oxygen from oxide-minerals (e.g. Fe and Mn oxides) to process the organic matter for growth, and subsequently causes release of arsenic associated with the oxide-minerals to the aqueous phase.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Ashfaque, Khandaker

Advisor dc:contributor.advisor

• Charles F. Harvey.

• Civil and Environmental Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/42218
• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Identifier URI

http://dspace.mit.edu/handle/1721.1/42218

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/42218