Vulnerability of drinking-water wells in La Crosse, Wisconsin, to enteric-virus contamination from surface water contributions
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Resource Abstract:
Human enteric viruses can contaminate municipal drinking-water wells, but few studies have examined the routes by which viruses
enter these wells. In the present study, the objective was to monitor the municipal wells of La Crosse, Wisconsin, for enteric
viruses and determine whether the amount of Mississippi River water infiltrating the wells was related to the frequency of
virus detection. From March 2001 to February 2002, one river water site and four wells predicted by hydrogeological modeling
to have variable degrees of surface water contributions were sampled monthly for enteric viruses, microbial indicators of
sanitary quality, and oxygen and hydrogen isotopes. 18O/ 16O and 2H/1H ratios were used to determine the level of surface
water contributions. All samples were collected prior to chlorination at the wellhead. By reverse transcription-PCR (RT-PCR),
24 of 48 municipal well water samples (50%) were positive for enteric viruses, including enteroviruses, rotavirus, hepatitis
A virus (HAV), and noroviruses. Of 12 river water samples, 10 (83%) were virus positive by RT-PCR. Viable enteroviruses were
not detected by cell culture in the well samples, although three well samples were positive for culturable HAV. Enteroviruses
detected in the wells by RT-PCR were identified as several serotypes of echoviruses and group A and group B coxsackieviruses.
None of the well water samples was positive for indicators of sanitary quality, namely male-specific and somatic coliphages,
total coliform bacteria, Escherichia coli, and fecal enterococci. Contrary to expectations, viruses were found in all wells
regardless of the level of surface water contributions. This result suggests that there were other unidentified sources, in
addition to surface water, responsible for the contamination.
Citation
Title Vulnerability of drinking-water wells in La Crosse, Wisconsin, to enteric-virus contamination from surface water contributions