| Summary: | During the 1980’s millions of households in Bangladesh switched from drinking surface water to private groundwater wells to reduce their exposure to fecal microorganisms. Sadly, this switch to shallow groundwater resulted in the largest example of drinking water poisoning in history, with approximately 100 million people exposed to high concentrations of naturally occurring Arsenic in the groundwater. Spatial distribution of Arsenic in the shallow aquifers tends to be patchy, so the most economical mitigation option has been lateral switching from high Arsenic wells to nearby low Arsenic wells. The recently developed Arsenic flushing conceptual model, which explains the spatial distribution of Arsenic throughout the shallow aquifers in Bangladesh, suggests however, that low Arsenic zones are recharged via coarse-grained, rapid flow pathways and therefore represent a higher risk for waterborne pathogens.
The objectives of this dissertation are to evaluate new methods for sampling and detection of waterborne pathogens, while also identifying sources of fecal contamination and transport pathway(s) to private wells emplaced within the shallow aquifers. It was demonstrated that private wells are broadly contaminated with E. coli, with prevalence ranging from 30 to 70%. The fact that E. coli was detected more frequently in private wells than sealed monitoring wells (p<0.05) suggests that well construction and/or daily pumping contribute to fecal contamination of the private wells. Using DNA-based molecular fecal source tracking, contamination was demonstrated to originate from human fecal waste. Unsanitary latrines, which spill effluent onto the open ground, were demonstrated to cause elevated levels of fecal bacteria in ponds, found in every village. These ponds were demonstrated to have an influence on concentrations of fecal bacteria to at least distances of 12m into the adjacent aquifer. In a culture where latrines, private wells and ponds are frequently clustered closely together, these findings suggest that improvements in the management of human fecal waste changes in placement and construction of private wells could substantially reduce exposure of people to fecal pathogens. Fecal contamination was found to be pervasive in low Arsenic, unconfined, shallow aquifers, and therefore gains from well switching to avoid Arsenic need to be balanced with the risk of consuming waterborne pathogens.
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