A Combined Hydrogeologic/Geochemical Investigation of Groundwater Conditions in the Waukesha County Area, WI

This report describes work done to ascertain the overall flow and geochemical conditions within the deep sandstone aquifer of southeast Wisconsin. The study focused particularly on Waukesha county, an area that is experiencing severe overpumping of the aquifer and contains several wells that produce water with radium activities in excess of the USEPA mandated limit of 5 pCi/L total radium. The affected municipalities are facing the possibility of EPA imposed fines, of installing expensive water treatment procedures or developing an alternate source of radium-free water. An understanding of radium behavior in this aquifer is very important to the affected communities.

High radium activities in Waukesha county occur along a band roughly parallel to and east of the Maquoketa subcrop. Previous workers were able to show that the generally low radium activities found in the aquifer to the west of the Maquoketa subcrop are controlled by co-precipitation into barite, but could not identify the cause of high activities found east of the subcrop (Grundl and Cape, 2006). This report is an extension and refinement of several earlier studies completed in southeastern Wisconsin (Clayton, 1999; Schmidt, 2002; Feinstein, et al., 2005; Grundl and Cape, 2006;). The overall hydrologic/geochemical conditions established in these earlier studies are used as a backdrop for a detailed investigation into the causes behind the high radium activities (in excess of 5 pCi/L) found east of the Maquoketa subcrop in Waukesha county. A final outcome of this work is the delineation of an isotopic and noble gas signature of these waters that is indicative of Pleistocene recharge. Implications as to the age and recharge dynamics beneath glaciated sediments are discussed.