Version history for SIM 3042 U.S. Geological Survey Base of Principal Aquifer for the Elkhorn-Loup Model Area, North-Central Nebraska Version 1.0: Posted On-line October 2008. Version 1.1: Posted On-line June 24, 2009. The map (base of aquifer contours, test hole locations, and registered well locations),report text, and associated data files were modified to reflect the findings from twelve new test holes drilled in summer 2008 and to correct errors in version 1.0 of the report.