1. U.S. Environmental Protection Agency, Office of Research and Development (E343-04), Research Triangle Park, North Carolina 27711, ARCADIS U.S., Inc., 4915 Prospectus Drive, Suite F, Durham, North Carolina 27713, and Centro Nacional de Investigación y Capacitación Ambiental, Instituto Nacional de Ecología, Av. San Rafael Atlixco 186, Col. Vicentina, Mexico, D.F. 09340