Microbial Transport Under Riverbank Filtration

The presence of microbial pathogens in surface and groundwater is a major environmental issue all around the world. Increased urbanization coupled with inadequate treatment of domestic and municipal wastes has resulted in contamination of precious water reserves across the globe. Riverbank filtration (RBF) was conceived back in the 1800's and is now commonly used for drinking water production. In the United States, it is estimated that around 70 million individuals are served by RBF systems. RBF is a simple and low-cost approach to remove particulates and microorganisms from surface water and make subsequent disinfection treatment easier. Waters of different chemistries mix during bank filtration, resulting in complex interactions between soil, bacteria, pollutants, and dissolved solids. The success of RBF can, however, depend on the hydrogeologic setting, source water quality, and river dynamics. During bank filtration, organic solids in the river water are strained out into alluvial sediments. In humid climates, bank filtration has been shown to remove the majority of dissolved organic constituents and heavy metals. Although bank filtration has been successful in humid climates, there is little data from arid climates. RBF technology can be more difficult to apply in arid environments because of the arid climate, heterogeneous sand-dominated river deposits and possibly long-term salt accumulation in the sediments. A tracer study was conducted to understand microbial contaminant transport under RBF conditions in the arid Rio Grande alluvium. The site was unique since it was located in an arid region and uses the Rio Grande river system that experiences significant fluctuations in both water quantity and quality. The results from the tracer study suggest that even in a relatively homogeneous aquifer, preferential transport within the aquifer can result in highly divergent microbial contaminant transport paths and rates.