1. Postdoctoral Fellow, Dept. of Envir. Engrg., Inha Univ., 253 Yonghyun-Dong, Nam-Ku, Inchon 402-751, Korea. E-mail: seongwon@inha. ac.kr
2. Asst. Prof., Dept. of Envir. Engrg., Inha Univ., 253 Yonghyun-Dong, Nam-Ku, Inchon 402-751, Korea. E-mail: hwangyw@inha.ac.kr