Collaborative Research: Arsenic Contaminated Groundwater in Bangladesh: Characterizing the Source, Mobilization and Transport

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0001098Harvey The drinking water of Bangladesh is severely contaminated with arsenic. Over one-half of the approximately four million wells that constitute the country's drinking water supply have levels of naturally occurring arsenic above the World Health Organization's standard of 0.01 mg/L, exposing as many as 50 million people to dangerous levels of arsenic in their drinking water. Concentrations as high as 0.5 mg/L are common. It has been suggested in the popular media [New York Times, November 10, 1998] that this may be the largest mass poisoning in history. Our primary research question is: What causes high levels of arsenic in the groundwater of Bangladesh? If the source, fate and transport of arsenic in the environment are not understood, future water management schemes run the risk of compounding the problem. We will test a set of working hypotheses for the cause(s) of arsenic contamination that include : (A) Depositional explanations for the distribution of solid and dissolved arsenic; (B) Geochemical/hydrologic reasons for high dissolved arsenic concentrations; and (C ) Anthropogenic causes of arsenic mobilization. From this understanding of the cause of high levels of dissolved arsenic, we will consider how arsenic concentrations may change in time and how arsenic is distributed throughout the country. Specific issues include: (A) Are arsenic concentrations correlated with particular sedimentary characteristics or surface hydrologic characteristics? (B) Can we develop better methods to site wells by interpolating arsenic concentrations from sampled locations? (C ) Do arsenic levels rise due to pumping or infiltration of fertilizers? (D) Can deep wells provide a long-term solution? The installation of deep wells has already begun on an ad hoc basis. We will conduct field and laboratory experiments, coordinated with modeling exercises, focusing on a cluster of 15 wells that range in depth between 3 m and 200 m installed in the Munshiganj district. We have also extracted a 200-meter core of solid aquifer material isolated from the atmosphere to maintain the redox state, perhaps the key control on arsenic activity. We will study the mechanisms that bind arsenic by analyzing the sediments and pore water with methods including X-ray adsorption spectroscopy (XAS), micro-probe analysis and growth of bacterial cultures, as well as sequential extraction of the preserved sediment samples. We will then study the effect of geochemical perturbations on arsenic mobilization in situ by injection-withdrawal tests from our installed wells using water that has been chemically altered to test hypothesized arsenic binding mechanisms. An understanding of arsenic binding mechanisms will support predictions regarding arsenic mobility and transport. Reactive-transport modeling will be used to consider mobilization due to pumping and redistribution by seasonal groundwater fluxes. Regional maps of arsenic concentration will be estimated by geostatistical methods constrained by knowledge of variations in sedimentary characteristics. Students and faculty will actively participate in the field, laboratory, and modeling work. To gain a sound scientific basis for long-term water management, we will convey our research to decision-makers to help provide safe drinking water for Bangladesh. This is a collaborative project with MIT, the University of Cincinnati, and Bangladesh University of Engineering and Technology.