The presence and transport of human enteric viruses in fractured bedrock aquifers

Abstract

Both onsite septic disposal systems and private drinking water wells are commonly utilized in rural areas of Canada. The coexistence of septic systems and drinking water wells has the potential to greatly impact the quality of water obtained in these settings. Human enteric viruses have been recognized as a potential source of groundwater borne disease, although the level of risk they pose and the processes responsible for their transport are poorly understood. As a result of thin overburden, low storage capacity, and high groundwater velocities, fractured rock aquifers are potentially at highest risk to viral contamination. However, only limited research has been conducted to explore this concern. The current study was conducted to investigate both the rate of occurrence of human viruses in fractured rock aquifers and the transport mechanisms acting in these settings. A survey was conducted to identify the prevalence of human enteric viruses in three fractured rock aquifers located across Canada. A total of 61 samples were collected from 28 wells drilled in aquifers in Ontario, Newfoundland, and British Columbia. Molecular PCR techniques were utilized to determine virus presence. Results showed that 37.7% of samples and 58.1% of wells were at some time positive for viruses. Virus presence was found to increase with housing density and viruses were found to travel distances of at least 40 meters. Poor correlation was found between the presence of viruses and traditional bacterial indicators. A field-scale viral infiltration experiment was conducted to investigate viral transport behavior. The bacteriophage ф-X174 and the fluorescent dye Lissamine FF were utilized as viral and solute tracers, respectively. Tracers were applied to an exposed rock outcrop exhibiting fractures with known connection to two nearby wells. Breakthrough was extremely rapid and the colloidal processes of decreased dispersion and slow-release kinetic sorption were identified. This study has provided concrete evidence that viral contamination poses a significant threat to fractured groundwater aquifers in rural areas where onsite septic disposal practices are utilized. The results observed in this study suggest that current set back distances and monitoring techniques may be inadequate to prevent exposure to human viruses.