USING AUTOSAMPLER MONITORING TO DETERMINE THE TIMING OF ENTERIC PATHOGEN CONTAMINATION OF THE FRACTURED SILURIAN AQUIFER, NORTHEASTERN WI

The fractured Silurian dolomite aquifer is an important, but vulnerable, source of water supply in rural northeastern Wisconsin. Dairy farming and associated crop production in this area comprise the primary land use and manure is commonly applied to crop land. As a result, this area has had long-term water quality problems with elevated nitrate, bacteria levels, and instances of non-potable "brown water" impacting domestic wells. Sporadic outbreaks of water-borne disease have focused attention on the presence of enteric pathogens in the aquifer. Historically there are no data available on the variability of pathogen loading or understanding of how pathogen transport relates to recharge events in this aquifer.

Our research seeks to determine the timing of enteric pathogen contamination of the Silurian aquifer in relation to groundwater recharge and nearby meteorological variables collected by others. We installed specialized autosamplers on three domestic water systems in order to collect detailed time-series of the concentrations of enteric pathogens and fecal microbial markers. The custom-built autosamplers, which could be triggered remotely to control sample collection, were programmed to continuously record the following water-quality parameters: fluid temperature and conductivity, chloride, nitrate, pH, and fluorescent dissolved organic matter (FDOM).

Two initial autosampler placements indicated considerable variability in total coliform counts over the course of recharge events, but yielded little information on other pathogens due to lack of a source term. A third placement, initiated as the spring recharge period was waning, also showed variability in total coliform counts. But more significantly, this location illustrated the variability of bovine Bacteroides and Rotavirus group A concentrations over time in response to small rainfall events.