Three-dimensional hydrostratigraphy of the Sprague,Nebraska Area: Results from Helicopter Electromagnetic (HEM) mapping in the Eastern Nebraska Water Resources Assessment (ENWRA) 2009 CB-4(NS), Dana P. Divine and Jesse T. Korus, 40 pp., size 8.5" x 11". 2012 Description: Groundwater resources under much of eastern Nebraska are contained within or beneath Quaternary glacial deposits. The heterogeneity and complexity of these deposits have hindered efforts to characterize them in detail. Test-hole drilling alone is not effective for mapping these units over large regions, but in certain settings, borehole data can be integrated with geophysical methods to map hydrostratigraphic units at high resolution and in three-dimensions. This study integrates test hole drilling and Helicopter Electromagnetic (HEM) surveys to characterize the hydrostratigraphy of an area around Sprague in southeast Nebraska. Helicopter Electromagnetic (HEM) surveys were flown in 2007 at three pilot study sites in eastern Nebraska as part of the ongoing Eastern Nebraska Water Resources Assessment (ENWRA), a collaborative study between six of Nebraska’s Natural Resources Districts, the Conservation and Survey Division (CSD) of the School of Natural Resources at the University of Nebraska-Lincoln, the Nebraska Department of Natural Resources (DNR), and the United States Geological Survey (USGS). The rationale and history behind ENWRA are outlined in Divine et al. (2009). The purpose of the pilot studies was to assess the effectiveness of HEM at mapping the complex geology of Quaternary alluvial and glacial deposits. The pilot studies were conducted at three sites that together encompass the wide range of hydrogeologic settings in eastern Nebraska. The Firth site, which is located adjacent to the Sprague area in the present study, overlies a paleovalley aquifer that is mantled by thick glacial deposits. Korus et al. (2012) demonstrated that major hydrostratigraphic boundaries in the upper 50 – 80 meters (approximately 160 – 260 feet) of the subsurface could be interpreted from HEM data in this geological setting. The results of the pilot study at Firth prompted resource managers to extend the study area to the west around the town of Sprague in southeastern Lancaster County. The results of the Sprague study are presented herein. Print on demand, color copy available.