Digital Models of a Glacial Outwash Aquifer in the Pearl-Sallie Lakes Area, West-Central Minnesota

The need for study of lake-ground-water interchange has been accentuated by eutrophication of lakes in the Pearl-Sallie Lakes area of west-central Minnesota. The local ground-water flow system is dominated by a sand and gravel outwash aquifer that is sandwiched between two layers of till in the western part of the area and exposed at the land surface in the eastern part. Water discharges from the aquifer into lakes in the outwash area but the aquifer is recharged from lakes in the till-covered area. Irregular aquifer geometry has resulted in a complex ground-water flow system. Simulation of the system by areal and vertical-section models has shown that the lakes significantly control ground-water flow near their shores. Inadequate field data and complex geology caused severe difficulty in obtaining solutions with the vertical-section model. Evaluation of the models has indicated that they may be used to guide field-data collection, interpretation of data, and quantification of the ground-water flow system. With modification, the models could be used to predict aquifer response to transient stresses. Also, they could be incorporated into more complex models, to determine the movement of solutes in the ground-water system.