Simulation of Ground-Water Flow and Delineation of Areas Contributing Recharge within the Mt. Simon-Hinckley Aquifer to Well Fields in the Prairie Island Indian Community, Minnesota

The Prairie Island Indian Community in east-central Minnesota uses ground water from the Mt. Simon-Hinckley aquifer as its source of water supply. Tribal officials implemented a Source Water Protection Program to protect the quality of this water. Areas of contributing recharge were delineated for two community well fields. At well field A are two wells 325 m apart, and at well field B are two wells 25 m apart. A steady state single layer, two-dimensional ground-water flow model constructed with the computer program MODFLOW, combined with the particle-tracking computer program MODPATH, was used to track water particles (upgradient) from the two well fields. A withdrawal rate of 625 m3/d was simulated for each well field. The ground-water flow paths delineated areas of contributing recharge that are 0.38 and 0.65 km2 based on 10- and 50-year travel times, respectively. The flow paths that define these areas extend for maximum distances of about 350 and 450 m, respectively, from the wells. At well field A the area of contributing recharge was delineated for each well as separate withdrawal points. At well field B the area of contributing recharge was delineated for the two wells as a single withdrawal point. Delineation of areas of contributing recharge to the well fields from land surface would require construction of a multi-layer ground-water flow model.