CHARACTERIZATION OF PREFERENTIAL FLOW PATHWAYS IN A SILICICLASTIC AQUIFER SYSTEM USING HUMAN ENTERIC VIRUSES AND GROUNDWATER GEOCHEMISTRY

Human enteric viruses have been recognized as an emerging groundwater contaminant and are found only in human waste. In urban environments the most likely source of human waste is from sanitary sewers. Determining the travel time for near-surface contaminants to reach deep public supply wells is important because viruses are only infectious in the groundwater environment for 1-2 years. This research utilized time-sequenced sampling of groundwater at discrete depths to detect human enteric viruses and geochemical parameters. The goal was to determine the factors by which a well is likely to become contaminated by sewer-derived wastewater. Virus sampling required pumping 800-1,000 L of groundwater through electropositive glass wool filters. Real time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) methods were used to determine the virus genome concentrations for adenovirus, rotavirus, enterovirus, hepatitis A virus, and norovirus genogroups I and II. Geochemical analyses included major ions, electrical conductivity, temperature, and pH.

Microbiological and chemical wastewater indicators were found at various depths in the aquifer system and in the well. These data improve the understanding of how wastewater may rapidly travel from a sanitary sewer into a deep confined aquifer and reach a public supply well. The combination of geochemical and virus data builds support for a conclusion that bedrock fractures create the preferential flow pathways that allow contaminants to rapidly reach a deep well. These types of fractures may also be present in other aquifer systems but their contribution to groundwater flow and transport may not be appreciated.