DOCUMENTING GROUNDWATER RESOURCES IN WISCONSIN’S CHEQUAMEGON-NICOLET NATIONAL FOREST: SUCCESSES AND CHALLENGES

Historically, groundwater assessments in U.S. National Forests have been rare, but groundwater information is essential to provide a baseline for decision making and forest plan development. The Wisconsin Geological and Natural History Survey, U. S. Geological Survey, and U.S. Forest Service (USFS) recently completed a cooperative assessment of groundwater resources in National Forest units in Wisconsin. The forest posed significant challenges for this work related to size, geologic variability, remoteness, access, lack of existing data, climate variability, transience, and incomplete geologic mapping.

The multi-year study involved four components designed to overcome these challenges in producing regional information and interpretations:

1. An inventory of geologic and hydrogeologic data for each forest unit, including basic hydrogeologic properties such as aquifer thickness, hydraulic conductivity, and transmissivity.
2. Recharge estimation using a soil water balance approach based on existing climatic, topographic, soils, and land-use data.
3. A summary of synoptic groundwater and surface water chemistry, including stable water isotope data intended to distinguish groundwater from surface water.
4. Construction of regional groundwater flow models using an analytic element code to provide a quantitative framework for the groundwater systems including model-generated water-table maps for each forest unit.

Although not areally extensive, the water sampling program provided a reasonable and previously unavailable baseline for basic water quality parameters in the forest, especially for groundwater. These delineations were generally consistent with characteristics of the groundwater flow systems identified during groundwater modeling. Stable isotopes proved useful in identifying several drinking water wells at campgrounds and picnic areas that were producing water from nearby surface water sources.

The flow models generated water-table maps for each unit and provided a check on the soil-water balance recharge estimates. These products allow USFS to generate simulated groundwater flow paths – both directions and estimates of time of travel. These models and supporting data sets provide quantitative starting points for future more detailed investigations of specific areas in the forest.