EFFECTS OF CLIMATE ON SUBSURFACE FATE AND TRANSPORT OF VIRUSES

Water wells and sanitary sewers are critical components of urban infrastructure, but leakage of untreated wastewater threatens groundwater quality. Previous work by our group documented infectious human enteric viruses in deeply-cased supply wells, and that leaking sewers were the likely source of such viruses. In order to investigate the temporal and spatial distribution of enteric viruses in shallow groundwater, seven field sites were established in southern Wisconsin. The sites represent a mix of urban and suburban settings, with sewer pipes ranging from 10 to 75 years old. Twenty-two wells were sampled 24 times over a twelve month period in 2012 and analyzed for enteric viruses. Influent to the regional waste water treatment plant was also sampled and analyzed.

The over-all virus detection rate in 2012, 3.7 % (17 of 455 samples), was much lower than the 43% (67 of 147) rate observed in 2008, when a subset of these wells was sampled. Surprisingly, sites close to newer sewers and those located within dense networks of old sewers had similar rates of virus positive samples. Virus concentrations were generally higher in shallow wells than in deep wells, but the rate of virus positive samples was similar in shallow and deep wells. The data are temporally correlated, suggesting that variations in climatic conditions affect virus transport. One of 130 groundwater samples collected during a summer drought was virus positive. The detection rate rose to over 7% (16 of 212 samples) during cool and wet conditions in the fall and winter. Although spring recharge resulted in two meters of water table rise, none of the 130 groundwater samples collected during this period were virus positive. Elevated water table conditions coincided with lower virus concentrations in untreated sewage, suggesting that infiltration to sewers may dilute wastewater and reduce virus concentrations in groundwater.

Results from this study suggest that several variables, including precipitation, recharge, and soil temperature, affect the fate and transport of viral pathogens from leaking sewers to the water table. Understanding conditions favorable to contaminant transport from sewers is important for characterization of well vulnerability to pathogens and to assess the value of sanitary sewer maintenance.