A 3-year study to determine the groundwater potential of confined glacial aquifers in a large part of Allen County, Ind., was begun in July 1974 by the U.S. Geological Survey. Mapping of outwash sands and gravels delineated two distinct layers of sand and gravel in the southern and eastern parts of the county that merge into one aquifer more than 100 feet thick to the north and west. A digital model that simulates groundwater flow in three dimensions was used to integrate the geologic and hydrologic conditions into a suitable analog of the groundwater system surrounding Fort Wayne. The model consisted of three layers representing (1) the upper till, (2) the upper sand and gravel, and (3) the lower aquifer. The lower aquifer represents a combination of the lower sand and gravel and a section of limestone aquifer immediately underlying the glacial sediments. The model, calibrated against water-level and streamflow data collected during September 1976, was used to simulate pumping and to evaluate the effects of pumping on groundwater levels and streamflows. Two distribution schemes of pumping were tested, each with two different boundary conditions (constant heads and constant flows). The results of these simulated pumping schemes indicate that between 30 and 40 million gallons per day can be produced and that the streamflow losses resulting from this pumping would be between 17 and 25 million gallons per day. (USGS)
