MODELING THE IMPACTS OF MINING ON HYDROLOGY IN THE ST. LOUIS RIVER BASIN

The St. Louis River Basin (SLRB) in northern Minnesota is not only home to the Mesabi Iron Range, but it is also territory ceded by the Tribes of this region, who maintain rights to hunt, fish, and gather on this land. Mining has the potential to alter groundwater flows that feed rivers, wetlands, and lakes. However, broad understanding of flows between ground- and surface-waters across the basin is limited.

In cooperation with Tribal representatives from five bands of Minnesota Chippewa and Ojibwe, the U.S. Geological Survey is developing a series of groundwater models for the SLRB to explore how groundwater flux to streams may have changed as a result of changing land uses. We use a stepwise approach, beginning with a broad two-dimensional analytic element model of the entire basin. We then zoom in to the Iron Range with a more detailed three-dimensional (3-D) finite-difference (MODFLOW) model. This 3-D model describes both horizontal and vertical flow of groundwater, providing information about groundwater/surface-water flows. Two 3-D models are being developed — one calibrated to modern conditions and one simulating the pre-iron-mining landscape. Comparison the results from these two models will allow us to estimate changes that have occurred in the groundwater flow system due to iron mining.

This study will provide those interested in land-use change effects on groundwater hydrology with a tool for understanding flow changes throughout a large area of the SLRB and will offer a resource to provide boundary conditions to site-specific models throughout the basin.