GROUND-WATER SUSCEPTIBILITY IN THE ST. CROIX RIVER BASIN, WISCONSIN AND MINNESOTA

Paul Juckem, U.S.G.S. Wisconsin Water Science Center

Understanding the susceptibility of ground water to potential contamination is important for managing water resources in the Saint Croix River Basin. In 2005, the U.S. Geological Survey, in cooperation with the National Park Service, developed an analytic-element ground-water screening model (GFLOW) and databases containing hydrogeologic information (for example, well locations with water level and geologic contact altitudes) for the Saint Croix River Basin (Feinstein et al., 2005). Recently, the databases and other state and regional maps were integrated to produce a map of ground-water contamination susceptibility in the St. Croix River Basin. The map is an improvement over similar maps of Minnesota and Wisconsin in that a single method (Schmidt, 1987) was applied across state boundaries, and local well data from the existing databases were used to improve input maps consisting of depth to water and depth to bedrock. The result is a map showing relative susceptibility of ground water to possible contamination due to human activities at the land surface. The original GFLOW model was refined for five subbasins (Kettle, Snake, Sunrise, Apple, and Kinnickinnic River Basins) to evaluate the pathways of potential contaminants once they reach the water table. Maps of simulated results show areas of relatively long and relatively short travel times for contaminants to reach nearby surface-water features. In addition, the GFLOW model was used to identify locations where potential contaminants in a river could move into the ground-water system. Simulated river reaches where surface water (and potential contaminants) move into the ground-water system are of limited extent and typically occur near areas with steep hydraulic gradients, such as near dams and waterfalls. The results of this work should be useful for managers who are charged with protecting water resources in the Saint Croix River Basin.

References

Feinstein, D.T., Buchwald C.A., Dunning C.P., and Hunt R.J., 2005, Development and Application of a Screening Model for Simulating Regional Ground-Water Flow in the St. Croix River Basin, Minnesota and Wisconsin, U.S. Geological Survey Scientific Investigations Report 2005-5283, 41 p.

Schmidt, R.R., 1987, Wisconsin’s Groundwater Management Plan, Report no. 5, Groundwater Contamination Susceptibility Map and Evaluation, Wisconsin Department of Natural Resources, 27 p.