1. Program of Interdisciplinary Research in Contaminant Hydrogeology, Department of Chemical Engineering, University of Virginia, Charlottesville, Virginia 22904-4741, U.S. Department of Defense, Charlottesville, Virginia 22911, Department of Chemical Engineering, Bucknell University, Lewisburg, Pennsylvania 17837, and Department of Civil Engineering, University of Virginia, Charlottesville, Virginia 22904-4741