Project:

Geologic, Hydrologic, and Geochemical Characterization of the
Deep Ground Water Aquifer System In the Bengal Delta of Bangladesh

Most of the highly arsenic-contaminated wells in the delta are completed in the "shallow aquifer", which commonly lies at a depth of 50-150 feet below the surface. Due to the complex sedimentologic nature of the delta, it is difficult to predict whether or not the zone of high arsenic is hydrologically separate from the deeper aquifer system. The deeper aquifer systems within the delta have been shown to contain nearly arsenic-free water, and thus they are a largely untapped source of potential drinking water for people in Bangladesh. The deeper aquifer systems are probably the most valuable unused natural resource in the country, yet a detailed understanding of the groundwater quality and quantity in these systems does not yet exist. Before this valuable resource can be exploited, it is essential to understand whether or not the deeper aquifer systems will remain arsenic free if developed over time.

During January 2002, the Government of Bangladesh (GOB) sponsored an International Workshop, which resulted in recommendations for providing alternative sources of safe water. Possible sources of safe water include rainwater, surface water, and deep ground water in addition to new or revamped water-treatment and water-distribution systems. The current project addresses the recommendations for using additional water wells, completed in both shallow and deep aquifers, as sources of safe water. The United States Geological Survey has been asked by USAID and US State Department, Dhaka to assist the government in Bangladesh in developing a strategy to better understand the ground-water arsenic situation and in particular to study possible alternative sources of clean water.

The USGS is currently conducting research on the deeper aquifer system in Bangladesh in areas associated with high levels of arsenic in the shallow ground water. The work uses an integrated geologic, hydrologic, microbiologic, and geochemical approach to characterize the deep aquifer system and to develop mappable criteria that will identify sources of safe ground water. This work is an integral step in the characterization of the hydrogeological framework needed to define the potential for developing safe and sustainable ground water sources. The important questions to address are, "To what extent can the deep aquifer system of the delta be reliably used to provide an alternative drinking-water source for the Nation?"; "How much good-quality water can be produced from this resource?"; and, "How long will it last?".

The answers to these questions are scientifically challenging, yet these answers are needed to justify the costs of developing this resource and to ensure that this resource is not knowingly, or unknowingly, contaminated. There are three general components to the current project, namely: (1) evaluation of the hydrology, geochemistry, microbiology, and geology of the deep aquifer at selected sites; (2) coordination of ongoing and planned work among several GOB agencies; and (3) capacity building. The USGS is working with many GOB agencies, other Donor Nations, International agencies and other interested parties to help better define the problem of developing an integrated system of ground water utilization and to develop methodologies to better understand the complexity of the natural hydrogeologic system.

Activities include:

• Test drilling, and aquifer testing in cooperation with the Bangladesh Water Development Board (BWDB)
• Core drilling and resistivity studies in cooperation with the Geological Survey of Bangladesh (GSB)
• Geophysical logging conducted in cooperation with Dhaka University Geology Department, and Columbia University
• Water sampling and analysis in cooperation with the Bangladesh Atomic Energy Commission (BAEC)
• XANES Analysis of sediments (micro-beam element/mineral analyses) with cooperation of Stanford University Synchrotron Radiation Laboratory (SSRL)
• Geochemical analysis of Borehole Sediments, including Optically Stimulated Luminescence Dating in cooperation with Dr. Steve Forman, University of Illinois at Chicago