April 2009 Meeting

Monday, April 13, 2009
6:00 - 7:30 pm

Pellissippi State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L. Goins Administration Building, Cafeteria Annex


Transport Pathways of Pathogens to Aquifers in Bangladesh

Peter Knappett, Larry McKay, and Alice Layton
University of Tennessee, Department of Earth and Planetary Sciences
Knoxville, Tennessee

In Bangladesh, switching drinking water sources from surface water to groundwater in the 1980&rsquos lowered diarrheal disease rates but tragically has resulted in the poisoning of millions of people by dissolved arsenic. The arsenic is widely believed to be derived locally from the natural alluvial sediments deposited by high energy rivers and floodplains. However, there is uncertainty about which factors (e.g., mineralogy, redox conditions, organic content, etc.) of the aquifer control the release of arsenic as a dissolved phase. One of the leading arsenic liberation models proposes that arsenic gradually increases with interstitial pore water residence time and hence is inversely related to groundwater recharge rates. If this model is correct the spatial pattern of arsenic will be controlled by the heterogeneous flood plain hydrogeology, with higher concentrations tending to occur in slow recharge areas, which are often overlain by fine-grained sediments. The mitigation practice of switching to wells with low arsenic concentrations, which typically are found in shallow, unconfined aquifers, raises the concern that decreasing exposure to arsenic will increase exposure to pathogenic bacteria and viruses. The purpose of the present research is to characterize the dominant transport pathways of fecal bacteria, viruses and pathogens to a sandy aquifer underlying a densely populated village where E. coli has been detected in 40-70% of private wells each month, peaking in the wet season. Initially, it was hypothesized that ponds are sources of fecal contamination to the shallow aquifer in both the dry and wet season, however monthly monitoring of monitoring wells next to ponds has ruled this out as a major dry season contamination source. The rapid draining of the ponds observed after heavy rain falls in the early monsoon indicates that the pond banks are quickly losing water to the surrounding aquifer and may still be an important source of bacteria and viruses to the aquifer. To test this hypothesis we plan to perform both natural and forced gradient experiments during the early monsoon in June.


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