This study is to improve the efficiency of BTL (Build Transfer Lease) project operation by comparing the infiltration rate based on the data of 5 years of infiltration of the separate sewer system and combined sewer system. In the survey site, the separate sewer system area consists of eight flowmeters in seven treatment basins, and the combined sewer system area consists of eight flowmeters in five treatment basins. The infillration rate was analyzed by night-time domestic flow evaluation method, and the average infiltration rates of the separate sewer system and combined sewer system were 13% and 16%, respectively. Combined sewer system was about 1.3 times higher than the separate sewer system. The average BOD of separate sewer system was 233 mg/L, which was about 2.4 times higher than the combined sewer system was 107 mg/L. In the comparison of the average pipe diameter-length infiltration of separate sewer system and combined sewer system, the separate sewer system and the combined sewer system were about 0.150 m3/d/mm/km and about 0.109 m3/d/mm/km, respectively. The floating population in mixed residential and commercial areas has been identified as the cause. Therefore, we propose a method to calculate the infiltration rate in consideration of the margin ratio in the area where the night active population is concentrated.

ABSTRACT
1. 서 론
2. 연구방법
    2.1 조사대상지역
    2.2 조사방법
3. 결과 및 고찰
    3.1 분류식 지역의 침입수량 분석
    3.2 합류식 지역의 침입수량 분석
    3.3 하수관로내의 수질 특성
    3.4 분류식과 합류식 지역의 침입수 발생 특성
4. 결 론
References

• 구광모(대전대학교 환경공학과/티에스케이워터) | Gwangmo Gu (Department of Enviromental Engneering, Daejeon University/TSK WATER)
• 저소웅(대전대학교 환경공학과) | Shaoxiong Chu (Department of Enviromental Engneering, Daejeon University)
• 임봉수(대전대학교 환경공학과) | Bongsu Lim (Department of Enviromental Engneering, Daejeon University) Corresponding author