Evaluation of Availability of Water From Drift Aquifers Near The Pomme De Terre and Chippewa Rivers, Western Minnesota

Ground-water flow in the confined- and unconfined-drift aquifers near Appleton and Benson, Minnesota, was simulated with a three-dimensional finite difference ground-water-flow model. Model results indicate that 98 percent of the total inflow to the modeled area is from precipitation. Of the total outflow, 38 percent is ground-water discharge to the Pomme de Terre and Chippewa Rivers, 36 percent is evapotranspiration, 17 percent is ground-water pumpage, and 8 percent is ground-water discharge to the Minnesota River. The model was used to simulate the effects of below-normal precipitation (drought) and hypothetical increases in ground-water development. Model results indicate that reduced recharge and increased pumping during a three year extended drought probably would lower water levels 2 to 6 feet regionally in the surficial aquifer and in the Appleton and Benson-middle aquifers and as much as 11 feet near aquifer boundaries. Ground-water discharge to the Pomme de Terre and Chippewa Rivers in the modeled area probably would be reduced during the simulated drought by 15.2 and 7.4 cubic feet per second, respectively, compared to 1982 conditions. The addition of 30 hypothetical wells in the Benson-middle aquifer near Benson, pumping a total of 810 million gallons per year, resulted in water-level declines of as much as 1.3 and 2.7 feet in the surficial and Benson-middle aquifers, respectively. The addition of 28 hypothetical wells in the Appleton aquifer east and southeast of Appleton, pumping a total of 756 million gallons per year, lowered water levels in the surficial and Appleton confined aquifers as much as 5 feet.