Depth-to-bedrock map analysis and preliminary deep aquifer assessment of Kewaunee County, Wisconsin

Author / Creator

Shea, Abby W., author

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Physical

Summary

The Silurian dolomite aquifer in northeastern Wisconsin has significant anthropogenic contamination. This upper aquifer is karsted in the study area, which, along with thin overlying unconsolidated...

The Silurian dolomite aquifer in northeastern Wisconsin has significant anthropogenic contamination. This upper aquifer is karsted in the study area, which, along with thin overlying unconsolidated sediments, contributes to water quality concerns, including viruses, excess nitrates, bacteria, and "brown water" incidents. Some wells in the northwestern portion of the county utilize the deeper, confined Cambrian-Ordovician sandstone aquifer, which is less susceptible to surface contamination. This aquifer has been increasingly utilized in parts of nearby counties for the past 30 years, however little is known about the groundwater chemistry of the aquifer in these areas. This study of 17 wells provides the first water quality analysis of the sandstone aquifer and its suitability to be used as an alternative water supply. The three primary objectives of this study, in order to overall improve our understanding of groundwater resources in and near Kewaunee County, were to analyze the usefulness of depth-to-bedrock maps, determine statistically significant predictors of depth-to bedrock map using soil properties, and to conduct a preliminary assessment of the groundwater quality of the deep, confined sandstone aquifer present in northeastern Wisconsin. The depth-to-bedrock map produced by Luczaj, Houghton and Shea (2019) (hereafter referred to as Luczaj et al. (2019)) yielded significant differences from historic maps. Statistical analyses showed many strong relationships, but also showed that the soil properties of interest cannot be used alone to definitively predict depth-to-bedrock. Piper plots of the confined sandstone aquifer show that the groundwater is of no dominant type, as cations exist in relatively equal proportions, as do anions, although some samples could be classified as sulfate type. Many samples exceeded various health standards, including strontium and radium. Despite various exceedances, the results reveal that the confined sandstone aquifer is a viable source of potable water in the study area along with a variety of treatment methods

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