ASSESSING THE OCCURRENCE OF VIRUSES AND BACTERIAL PATHOGENS IN UNTREATED WATER FROM MUNICIPAL WATER SUPPLY WELLS IN IOWA

The Iowa Department of Natural Resources, in cooperation with partners at Laboratory for Infection Disease and the Environment (an interagency laboratory between USDA-ARS and the USGS Wisconsin Water Science Center), the USGS Iowa/Illinois Water Center, and the State Hygienic Laboratory of the University of Iowa, has completed two rounds of sampling for viruses and bacterial pathogens in municipal water supply wells representing Iowa’s six major aquifer systems.

Sampling of untreated groundwater was first conducted at 66 wells in the spring of 2013, then at 94 wells in the fall/winter of 2016-2017. Samples were analyzed for seven human-specific enteric viruses, three animal-specific viruses, one plant virus, and three non-host-specific bacterial pathogens using qPCR. The overall frequency of detection of pathogenic organisms was higher in 2013 (23%) when shallow groundwater levels were generally increasing after a two-year drought, than in 2017 (6%) when shallow groundwater levels were declining in much of the state. Pepper mild mottle virus, a plant pathogen that occurs in human waste, was the most commonly detected virus in both years and also the virus with the highest reported concentration (26.7 gene copies/L). The human viruses, GII norovirus, human polyomavirus, and adenovirus C,D, F, were each detected once. Bovine polyomavirus was detected in two samples. Campylobacter was detected once. Adenovirus A, adenovirus B, enterovirus, GI norovirus, swine hepatitis E, avian influenza A, Salmonella, and enterohemorrhagic E. coli were not detected.

Detections occurred more frequently in wells defined as highly vulnerable to contamination from the surface (based on confining layer thickness) than in lower vulnerability wells. However, no significant correlations between pathogen detections and groundwater vulnerability were seen. As has been reported in other Midwestern studies, viruses were detected in wells screened in highly confined aquifers for which water quality parameters indicate long travel times. These results suggest that some water is able to enter wells either through preferential flow pathways and/or faulty well construction. No correlations were found between pathogen detections and other water quality parameters.