GOOD OR BAD NEWS? A DOSE OF HUMAN ENTERIC VIRUS TRACER MAY PROTECT YOUR MUNICIPAL DRINKING WATER SUPPLY

Recent work in Wisconsin has shown that human enteric viruses can migrate from leaking sanitary sewers into municipal wells at depths of 275 m on timescales of weeks to months. The absence of a consistent relationship between virus detection and environmental tracers such as Cl, δ¹⁸O, δ²H, and ³H, suggested the latter’s limited ability to predict viruses and thus protect public drinking water. In contrast, the viruses themselves, because of their small size and mobility, are nearly ideal tracers of rapid transport in groundwater. We observed virus tracers in the Ames aquifer, an alluvial/buried valley aquifer that supplies drinking water to Ames, Iowa (pop. 59,000). Our focus was the Downtown Well Field, where continuous pumping induces flow from the South Skunk River (SSR) nearly 1.4 km away. Because the watershed contains 14 wastewater treatment plants and 109 swine CAFOs, we hypothesized that human enteric viruses (and Hepatitis E viruses; HEV) would be drawn into the well field from the SSR. Hydraulic data corroborated this relationship and predicted that viruses would travel ~2 km in the aquifer within two years; thus, the experimental design consisted of four sampling sites along a groundwater flow path at distances of 3.1 m to 2 km from the SSR. We collected 48 samples for Cl, δ¹⁸O, and δ²H and for adenovirus, enterovirus, norovirus, rotavirus, and HEV during seven sampling events (October 2011 to October 2012). We sampled untreated sewage (twice) and ³H from groundwater (once). Viruses were analyzed using RT-qPCR methods. Results showed that traditional tracers became uniform away from the river, but at least one virus was detected in 42% of the samples, with groundwater showing at least one detection in sites out to 2 km and in 34% of the samples overall. Adenovirus Subgroup A and HEV were the most frequently detected. Sewage samples showed higher concentrations of adenovirus Subgroups A and C, D, F, but no HEV. Serotyping showed adenovirus A31 in the SSR and sewage, but swine HEV only in the SSR. We conclude that the SSR is the source of swine HEV and adenovirus A31 in the aquifer, thus confirming our hypothesis and showing the potential use of virus tracers to protect drinking water. Adenovirus Subgroup C, D, F in sewage could be a useful tracer of vertical leakage through poorly constructed municipal wells in the overlying aquitard.