Seismic refraction methods have been extensively used in petroleum, mineral, and engineering investigations, and to some extent for hydrologic applications, during the past 30 years. Recent advances in equipment, sound sources, and computer interpretation techniques make seismic refraction methods highly effective and economical for obtaining data for groundwater modeling studies. Aquifers that can be defined by one or more seismic velocity surfaces, such as alluvial or glacial deposits in consolidated rock valleys, limestone, or sandstone underlain by metamorphic or igneous rock, or saturated unconsolidated deposits overlain by unsaturated unconsolidated deposits, are ideally suited for seismic refraction methods. Seismic refraction allows economical collection of data for one or more model input parameters and provides the basis for efficient collection of subsurface data by test drilling or aquifer tests. Seismic refraction studies were conducted over unconfined glacial aquifers in New England to determine: (1) depth of the underlying bedrock; (2) depth of the water table; (3) saturated thickness of the aquifer in areas not accessible to heavy drilling equipment; (4) areas where thick, unsaturated sediments overlie thickly saturated parts of the aquifer; and (5) locations of test holes and type of drilling equipment needed. These data were used in groundwater models and provided parameter values that required few adjustments during calibration.