Ground Water/Surface Water Interaction in Nearshore Areas of Three Lakes on the Grand Portage Reservation, Northeastern Minnesota, 2003–04

Abstract

This is a geologic and hydrological study of three lakes on the Grand Portage Reservation and is largely technical in scope. These three lakes have higher conductivity levels than other lakes in the Reservation. Public water comes from surficial water supplies, while ground water is used for private water sources such as wells, mainly within two miles from Lake Superior. Ground water is too saline to use for public water use. Results of the study show that water movement and quality in this geologically-fractured area are complex, and that lake sediment temperature monitoring may be the most reliable method for natural resources managers. Key findings from the report are extracted and reproduced below. “The availability of good quality water from lakes and wetlands on the Grand Portage Reservation in northeastern Minnesota is an important concern of the Grand Portage Band of Chippewa Indians. Development and changing land-use practices may affect the quality and quantity of water resources on the reservation. To effectively protect the water quality and quantity of the lakes and wetlands, an understand¬ing of exchanges between ground water and surface water on local and regional scales is needed. Numerous hydrologic studies have been done on the reservation, but none of these studies has focused on determining ground-water/surface-water interactions of lakes and wetlands. The U.S. Geological Survey (USGS), in cooperation with the Grand Portage Band of Chippewa Indians, conducted a study to assess ground-water/surface-water interactions in nearshore areas of three lakes, North, Teal, and Taylor Lakes on the Grand Portage Reservation in 2003 and 2004. These three lakes were selected on the basis of the rela¬tively high specific conductance values of water from these lakes compared to other lakes on the reservation. The high specific conductance values of the lake water may indicate that ground-water inflow is an important component of the water balance of the lakes. The objective of the study was to identify areas of ground-water inflow to the three lakes and surface-water outseepage to local aquifers through the assess¬ment of existing aerial photographs and water-quality data. Results from this study indicate that ground-water and surface-water interactions at the study lakes are complex, and the ability of the applied techniques to identify ground-water inflow and surface-water outseepage locations varied among the lakes. Measurement of lake-sediment temperatures proved to be a reliable and relatively inexpensive reconnaissance technique that lake managers may apply in complex settings to identify general areas of ground-water inflow and surface-water outseepage.”