Geometry and hydraulic characteristics of a 46.5 sq mi area of the sand and gravel outwash-aquifer system between Fawn and Pigeon Rivers in Lagrange County were defined in a study of the effect of current and potential uses of water on the aquifer, streams, lakes, and wetlands. There are three aquifers: Aquifer 1, a surficial water table aquifer that ranges from 10 to 60 ft in thickness, hydraulic conductivity of 210 ft/d, and transmissivity of 5,000 to 16,000 sq ft/day. Aquifer 2 ranges from 50 to 110 ft in thickness, hydraulic conductivity of 360 ft/d, and transmissivity ranges of 5,000 to 35,000 sq ft/day. Aquifer 3 ranges from zero to 200 ft in thickness, hydraulic conductivity of 25 ft/d, and transmissivity of zero to 5,000 sq ft/d. A three-layer digital flow model was calibrated to steady-state water levels during autumn 1982. The effects of current and potential development of irrigation on the groundwater and surface water systems were estimated by transient simulations of five pumping plans. The effect of year-round pumping was estimated by steady-state simulation of a sixth plan. Plan 1 was a simulation of current irrigational development with pumpage equal to that which supplied water to crops in 1982. Maximum simulated drawdowns were 4 ft in layer 1 and 14 ft in layers 2 and 3. Simulated drawdowns were greater than those observed in 1982. Plans 2 and 3 were simulations of the current irrigational development with pumping rates that would supply water to crops in a normal and in a dry year. The effect on the hydrologic system by pumping in plans 2 and 3, therefore, is minimal. Plans 4 and 5 were simulations of maximum potential irrigational development that would supply water to a corn crop during a normal and a dry year. The maximum simulated drawdowns for plan 4 were 14, 30, and 31 ft in aquifers 1, 2, and 3, respectively. Maximum drawdowns for plan 5 were 15, 32, and 31 ft in aquifers 1, 2 and 3.
