Characterization of the Hydrostratigraphy of the Deep Sandstone Aquifer in Southeatern Wisconsin

Introduction: Over the last century and particularly within the last 40 years, the region in southeastern Wisconsin encompassing the counties of Washington, Ozaukee, Waukesha, Milwaukee, Walworth, Racine and Kenosha, has undergone increasingly rapid urban and suburban development. Centers of population have grown rapidly in outlying counties in contrast to the central urban area of Milwaukee. The major source of municipal and industrial water supply has traditionally been the Cambrian-Ordovician aquifer system (Figure 1) known as the “deep sandstone” aquifer. However, as an increasing number of deep wells have been constructed in this aquifer (beneath the Maquoketa shale confining unit), the potentiometric surface has declined significantly, by several hundred feet since the turn of the century. Municipalities along the lakeshore have largely converted to water supplies from Lake Michigan, but inland counties continue to rely on groundwater from the Cambrian-Ordovician aquifer system because of limits on diversion of surface water out of the Lake Michigan basin.