1. Professor, Dept. of Environmental Engineering, Konkuk Univ., 1 Hwayang-dong, Gwangjin-gu, Seoul 143-747, Korea.
2. Professor, Dept. of Earth and Environmental Sciences, Sejong Univ., Goon Ja Dong 98, Gwang Jin Goo, Seoul 143-747, Korea.
3. Research Associate Professor, Dept. of Environmental and Civil Engineering, Southern Methodist Univ., P.O. Box 750340, Dallas, TX 75275-0340 (corresponding author).
4. Professor, Dept. of Materials Science and Engineering, Univ. of Maryland, 2309F Chem-Nuc, Engineering Bldg. #090, College Park, MD 20742-2115.