Scott Ikard, USGS Texas Water Science Center, Austin, TX, United States, Martin A Briggs, USGS Office of Groundwater, Hydrogeophysics Branch, Reston, VA, United States, Burke J Minsley, USGS Geology, Geophysics, and Geochemistry Science Center, Denver, CO, United States and John W Lane Jr, USGS, Hydrogeophysics Branch, Storrs, CT, United States