USING VIRUSES TO ASSESS SOURCES OF WASTEWATER CONTAMINATION IN RURAL NORTHEASTERN WISCONSIN: PRELIMINARY RESULTS

The fractured Silurian aquifer is an important, but vulnerable, source of water supply in rural northeastern Wisconsin. Voluntary sampling programs over the last decade indicate that half of the domestic wells in the Town of Lincoln in Kewaunee County do not meet drinking-water standards, due to either the presence of bacteria and/or exceedance of the US EPA nitrate standard. As resource managers try to address these water-quality problems, there is no consensus as to whether the main source of contamination is human or bovine wastewater. In this area, dairy farming and associated crop production comprise the primary land use and manure is commonly applied to crop land. Nutrient management plans indicate approximately 13,500 cattle within the Town of Lincoln (land area = 35.7 mi²). The Town has approximately 334 households and all homes have either a holding tank or a private septic system.

We completed a pilot project to assess whether sampling private wells for viruses could be an effective method of assessing sources of wastewater impacts in the Town of Lincoln. Virus sampling was conducted over 2 ½ days in late May and involved pumping ~800 L of groundwater through hemodialysis filters. Real time quantitative reverse transcription-polymerase chain reaction (RT-qPCR) methods were used to determine the virus genome concentrations for both bovine-specific and human-specific viruses. In addition, samples were analyzed for pepper mild mottled virus (indicative of contamination from ground surface), bovine bacteroides, and zoonotic pathogenic bacteria that can be derived from either human or bovine fecal waste: enterohemorrhagic E. coli, Salmonella species, and Campylobacter jejuni.

Results indicate that seven of the ten sampled wells were positive for fecal contamination. Two wells contained human-specific viruses, one well contained bovine-specific viruses, one well contained both virus types, and one well was positive for bovine bacteroides. Five of the wells contained either Salmonella or C. jejuni which is concerning in terms of human health. We are currently designing a longer term study to better assess the source of the viruses and bacteria. Study design is complicated by the fact that recharge to the dolomite aquifer is extremely rapid and water quality is also highly variable in response to the rapid recharge.