Submitted to: Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/18/2010
Publication Date: 9/7/2010
Citation: Hunt, R.J., Borchardt, M.A., Richards, K.D., Spencer, S.K. 2010. Assessment of Sewer Source Contamination of Drinking Water Wells Using Tracers and Human Enteric Viruses. Environmental Science and Technology. Environ. Sci. Technol.44:7956-7963.. Interpretive Summary: High-capacity wells pump large volumes of groundwater for uses such as municipal drinking water and crop irrigation. When the pump is turned on, groundwater and any contaminants located within the water are pulled into the well from the contributing area for the well. Users and regulators of these wells are often confronted with the question, “Is this well vulnerable to contamination?” This study showed that multiple water samples are necessary to evaluate well vulnerability; if only one sample is collected, the results likely underestimate the true potential for contamination. Moreover, the types of contaminants found in wastewater (pharmaceuticals, pesticides, plasticizers, and pathogens, to name a few) differ greatly in our ability to detect them. Their concentrations at contamination sources, and their behavior underground, are different so that any information on the contamination potential of one type of contaminant does not necessarily translate to another type. Lastly, the standard approach for assessing well vulnerability is to measure average properties of groundwater flow, like velocity and time-of-travel, assuming that contaminants move with the water. However, contaminants that are very small particles, like human viruses, can travel faster than the bulk water. Faster travel time may mean the contaminant does not have time to degrade underground before it leaves the well and is ingested by a person or animal. This information will help users of high-capacity wells, such as drinking water utilities and irrigators, avoid well water contamination from human or livestock wastewater.
Technical Abstract: This study investigated the source, transport, and occurrence of human enteric viruses in municipal well water, focusing on sanitary sewer sources. A total of 33 wells from 14 communities were sampled once for wastewater tracers and viruses. Wastewater tracers were detected in 4 of these wells, and 5 wells were virus- positive by qRT-PCR. These results, along with exclusion of wells with surface-water sources, were used to select three wells for additional investigation. Viruses and wastewater tracers were found in the groundwater at all sites. Some wastewater tracers, such as ionic detergents, flame retardants, and cholesterol, were considered unambiguous evidence of wastewater. Sampling at any given time may not show concurrent virus and tracer presence; however, given sufficient sampling over time, a relation between wastewater tracers and virus occurrence was identified. Presence of infectious viruses at the wellhead demonstrate that high-capacity pumping induced sufficiently short travel times for the transport of infectious viruses. Therefore, drinking-water wells are vulnerable to contaminants that travel along fast groundwater flowpaths even if they contribute a small amount of virus-laden water to the well. These results suggest that vulnerability assessments need to include characterization of “low yield-fast transport” in addition to traditional “high yield-slow transport”, pathways.