BACKGROUND: Groundwater quality in the Silurian dolomite aquifer in northeastern Wisconsin, USA, has become contentious as dairy farms and exurban development expand. OBJECTIVES: We investigated private household wells in the region, determining the extent, sources, and risk factors of nitrate and microbial contamination. METHODS: Total coliforms, Escherichia coli, and nitrate were evaluated by synoptic sampling during groundwater recharge and no-recharge periods. Additional seasonal sampling measured genetic markers of human and bovine fecal-associated microbes and enteric zoonotic pathogens. We constructed multivariable regression models of detection probability (log-binomial) and concentration (gamma) for each contaminant to identify risk factors related to land use, precipitation, hydrogeology, and well construction. RESULTS: Total coliforms and nitrate were strongly associated with depth-to-bedrock at well sites and nearby agricultural land use, but not septic systems. Both human wastewater and cattle manure contributed to well contamination. Rotavirus group A, Cryptosporidium, and Salmonella were the most frequently detected pathogens. Wells positive for human fecal markers were associated with depth-to-groundwater and number of septic system drainfield within 229 m. Manure-contaminated wells were associated with groundwater recharge and the area size of nearby agricultural land. Wells positive for any fecal-associated microbe, regardless of source, were associated with septic system density and manure storage proximity modified by bedrock depth. Well construction was generally not related to contamination, indicating land use, groundwater recharge, and bedrock depth were the most important risk factors. DISCUSSION: These findings may inform policies to minimize contamination of the Silurian dolomite aquifer, a major water supply for the U.S. and Canadian Great Lakes region.

Experiences with many measurements of the hydraulic conductivity of unlithified glacial and fluvial materials in Wisconsin suggest that hydraulic conductivity must be viewed in terms of the operational scale of measurement, based on the scale of the problem at hand and the volume of the materials of interest. Frequently, the hydraulic conductivity of a given lithostratigraphic unit appears to increase as the operational scale of measurement increases. In particular, laboratory methods can yield hydraulic conductivities one to two orders of magnitude lower than conductivities determined in field tests on the same materials. The operational scale of most laboratory methods is much smaller than the operational scale of most field problems, and laboratory tests, although often logistically and financially attractive, may be of little value in characterizing the hydraulic conductivity of Pleistocene and recent deposits at working field scales.

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BACKGROUND: Private wells are an important source of drinking water in Kewaunee County, Wisconsin. Due to the region's fractured dolomite aquifer, these wells are vulnerable to contamination by human and zoonotic gastrointestinal pathogens originating from land-applied cattle manure and private septic systems. OBJECTIVE: We determined the magnitude of the health burden associated with contamination of private wells in Kewaunee County by feces-borne gastrointestinal pathogens. METHODS: This study used data from a year-long countywide pathogen occurrence study as inputs into a quantitative microbial risk assessment (QMRA) to predict the total cases of acute gastrointestinal illness (AGI) caused by private well contamination in the county. Microbial source tracking was used to associate predicted cases of illness with bovine, human, or unknown fecal sources. RESULTS: Results suggest that private well contamination could be responsible for as many as 301 AGI cases per year in Kewaunee County, and that 230 and 12 cases per year were associated with a bovine and human fecal source, respectively. Furthermore, Cryptosporidium parvum was predicted to cause 190 cases per year, the most out of all 8 pathogens included in the QMRA. DISCUSSION: This study has important implications for land use and water resource management in Kewaunee County and informs the public health impacts of consuming drinking water produced in other similarly vulnerable hydrogeological settings.

We measured net nitrate retention by mass balance in a 700-m upwelling reach of a third-order sand plains stream, Emmons Creek, from January 2007 to November 2008. Surface water and groundwater fluxes of nitrate were determined from continuous records of discharge and from nitrate concentrations based on weekly and biweekly sampling at three surface water stations and in 23 in-stream piezometers, respectively. Surface water nitrate concentration in Emmons Creek was relatively high (mean of 2.25 mg NO 3 -N l -1 ) and exhibited strong seasonal variation. Net nitrate retention averaged 429 mg NO 3 -N m -2 d -1 and about 2% of nitrate inputs to the reach. Net nitrate retention was highest during the spring and autumn when groundwater discharge was elevated. Groundwater discharge explained 57-65% of the variation in areal net nitrate retention. Specific discharge and groundwater nitrate concentration varied spatially. Weighting groundwater solute concentrations by specific discharge improved the water balance and resulted in higher estimates of nitrate retention. Our results suggest that groundwater inputs of nitrate can drive nitrate retention in streams with high groundwater discharge.