Madison, Wisconsin: State of Wisconsin Department of Natural Resources
The salinity and major ion content of the water contained within the Cambro-Ordovician aquifer of eastern Wisconsin was investigated. Data obtained form the Wisconsin Department of Natural Resources Drinking Water Database in conjunction with stratigraphic data obtained from the Wisconsin Geologic and Natural History Survey was used to compile an overall view of geochemical conditions within the aquifer. All data was entered into GIS format (ArcView 3.2). Salinity of water pumped from the aquifer averages 473 ppm and is more saline to the north and east. The spatial variance in salinity is almost entirely due to a 1:1 molar increase in calcium and sulfate, probably due to dissolution of gypsum. In spite of this increase in calcium-sulfate character, the aquifer is dominated by calcium-bicarbonate water except in isolated locations within Calumet and Outagamie Counties where the water is calcium-sulfate in character. An attempt was made to correlate the percentage of the well open to a particular stratigraphic interval and salinity, however no correlation was found. Most wells within the study area do not exhibit large changes in salinity over time. Only 10 wells have salinity changes that exceed 10 ppm/year and of these, 5 exhibit decreasing salinities. Stratigraphic data are used to show the usage pattern of the Cambro-Ordovician aquifer. Maps are presented that show, on a relative basis, form which stratigraphic unit water is being pumped.