GroMoPo Metadata for Eastern Wisconsin geochemical model

A finite-difference ground-water flow model linked to a particle-tracking routine was used to determine ground-water flow paths and residence times in the Cambrian-Ordovician sandstone aquifer of eastern Wisconsin. The modeled region was a cross section along an approximate flow line that included the boundary between unconfirmed and confined conditions in the aquifer. Modeling results indicate that lower conductivity units within the sandstone aquiter produce vertically stratified flow in the confined region. These simulation results help explain chemical signatures of ground water in different parts of the aquifer. Three distinct regions of the flow system are identified: the unconfined zone where vertical mixing across the aquifer yields a homogeneous chemistry, the shallow part of the confined zone where sodium and sulfate charged water from the Maquoketa Shale mixes with water that has migrated from the unconfined area, and the deeper region of the confined aquifer, containing older water that entered the system in the unconfined area. Radium activities in ground water increase with distance along flow paths predicted by the simulation, consistent with a low concentration source of solid phase uranium and release of decay products to ground water by desorption and dissolution throughout the sandstone aquifer.