Dr. Susan Swanson Colloquia

Director, State Geologist Wisconsin Geological and Natural History Survey

Title: Threats to Groundwater Resources in the Chequamegon-Nicolet National Forest

Abstract: The Chequamegon-Nicolet National Forest (CNNF) in northern Wisconsin contains numerous groundwater-dependent water resources that may be vulnerable to potential effects of land development, mining, and climate change. The Wisconsin Geological and Natural History Survey (WGNHS) is working with the U.S. Forest Service and the Great Lakes Indian Fish & Wildlife Commission (GLIFWC) to assess current conditions and better understand these potential threats to groundwater resources in the CNNF. WGNHS recently inventoried groundwater resources in the four units of the CNNF (Park Falls, Medford, Nicolet, Washburn/Great Divide) to assess forest-wide water quality conditions. Samples from over 160 lakes, streams, and wells were analyzed for major ion chemistry in 2016 and again in 2021-22. Throughout the national forest, mostly non-carbonate unlithified glacial deposits overlie crystalline bedrock. As a result, concentrations of most ions in groundwater and surface waters are relatively low. Locally, elevated chloride suggests some influence from road salting. However, water quality in all four units of the CNNF is very good and considered pristine in many areas, thus highlighting its vulnerability to human activities in the future. Additional studies are further characterizing water chemistry and establishing baseline hydrogeologic conditions near the Bend Copper-Gold Deposit, a potentially viable deposit for mining. WGNHS is also investigating the vulnerability of seepage lakes to groundwater flooding. For the many seepage lakes and wetlands in the region, projected changes in the amount of precipitation and the frequency of extreme events brings flooding concerns from rising groundwater and threats to groundwater-dependent habitats. The subtle glacial topography of the region and variations in the elevation of the bedrock surface can lead to differences between surface flows and groundwater movement further complicating the prediction of these often prolonged flooding events. This talk will highlight results from these three projects, as well as provide an overview of the broader mission and work of the WGNHS.