Stratified fluvial sediments occur within the glacial drift at many places in the Mesabi Iron Range area. These sediments, which are important aquifers, occur extensively between the three main till units. The thickest and most extensive aquifer consists of glaciofluvial sediments that lie between the surficial till and the middle till unit, the bouldery till. Thickness of the glaciofluvial sediments at this stratigraphic interval is greater than 50 feet in much of the area, and transmissivity is greater than 100,000 gallons per day per foot in some places.
Glaciofluvial sediments underlying the bouldery till occur largely in the western half of the area. These sediments are generally less than 50 feet thick, and transmissivity is generally less than 50,000 gallons per day per foot.
Surficial glaciofluvial sediments are a source of ground water for high-yield wells only in the eastern part of the area in the vicinity of the Biwabik bedrock valley. Thickness of these sediments is greater than 100 feet in some places, but transmissivity is generally less than 50,000 gallons per day per foot.
Practical sustained yield of aquifers in glacial drift is estimated to be as much as 40 million gallons per day from known aquifers. Assuming that the ratio of area underlain by aquifer to total area is constant for the study area (about 20 percent where mapped in detail), as much as 80 million gallons per day could be developed from glacial-drift aquifers.
