Hydrogeology of Sand-Plain Aquifers in Carlton, Kanabec, and Pine Counties, East-Central Minnesota

Sand-plain aquifers in parts of Carlton, Kanabec, and Pine Counties in east-central Minnesota constitute a major aquifer system. They consist predominantly of fine to medium outwash sand with a combined areal extent of nearly 500 square miles. Saturated thickness in localized areas is as much as 90 feet. Depth to water generally is less than 20 feet. Transmissivities range from about 100 to 25,000 feet squared per day. Yields to properly constructed wells locally may exceed 2,000 gallons per minute. A reconnaissance of sandstone units underlying the outwash indicates that transmissivities of the sandstone aquifers range from 1,850 to 2,200 feet squared per day, and specific capacities range from 9 to 12 gallons per minute per foot of drawdown. Locally, wells may be capable of supplying several hundred gallons per minute. Regionally, the sand-plain and sandstone aquifers are poorly connected hydraulically at all locations tested except in a small localized area near Quamba in Kanabec County. Ground water in the sand-plain aquifers can be classified chemically, based on predominant ions, as a calcium bicarbonate type that is moderately hard. Concentrations of dissolved solids range from 30 to 610 milligrams per liter. Except for locally high concentrations of iron and manganese, the quality of water is within State drinking-water standards and is suitable for most uses. There are no major differences between the quality of water in the sand-plain and sandstone aquifers. Ground-water flow, aquifer response, aquifer development, and drought conditions were simulated for sand-plain aquifers areally extensive enough to be hydrologically significant. Simulation of expanded ground-water development and drought in northern Pine County indicates that regional ground-water levels may be lowered as much as 12 feet and ground-water discharge to streams may be reduced as much as 42 percent. Simulation of expanded development and drought in southern Pine County indicates that regional ground-water levels may be lowered as much as 25 feet and ground-water discharge to streams may be reduced as much as 65 percent. The simulations also indicate that each area, especially the northern Pine County area, will support substantial additional development without dewatering the aquifer or reducing streamflow significantly.