Long-term Alterations in Groundwater Chemistry Induced by Municipal Well Pumping

Background:
Dane County, Wisconsin, hosts a number of high-capacity, multi-aquifer wells that were drilled through the regional Eau Claire aquitard and draw from both the confined and unconfined aquifers. These wells are excellent study sites in which to test hypotheses related to pumpinginduced  hanges in redox conditions and mobilization of trace elements. Simulations with a recently revised county-scale flow model indicate that the presence of multi-aquifer wells and drawdown in the confined aquifer generated by decades of pumping have changed interactions between the confined and unconfined aquifers and between the surface and groundwater systems. Additionally, historical groundwater sampling of Madison Water Utility wells has revealed elevated hexavalent chromium, iron, and manganese in the groundwater from certain wells.
Objectives:
Objectives of this study were to further explore the impacts of pumping on induced mixing of groundwater from shallow and deep aquifers and to identify geochemical processes resulting from such mixing.