Existing sewer evaluation results and rehabilitation strategies: The City of Seoul, Korea

Abstract

A sewer evaluation study was conducted for the eight basins in the City of Seoul. The results indicated that the sewer system has a problem at every 5 m. This condition increases the amount of inflow and infiltration resulting in poor operation of the publicly owned treatment works (POTWs) which are owned and operated by the City. The study also identified that the following five defects as responsible for more than 87% of the problems: joint defects (27.5%), protruding lateral (21%), service connection defects (14.5%), sand/gravel debris (13.0%), and structural cracking (11.0%). In addition to the structural and hydraulic degradation, these problems are the main causes for an average inflow and infiltration of 109.4 m(3) hectare(-1) day(-1). To fix these problems, use of trenchless rehabilitation technologies are recommended considering the congested conditions of Seoul. It is estimated that an average of $95 800 per hectare is required for rehabilitation. For the entire Seoul system covering 605.9 km(2), a total rehabilitation cost is estimated of approximately 5.8 billion dollars. In addition, to increase the effectiveness of rehabilitation, recommendations are made including preparation of more detailed rehabilitation guidelines, specifying ways of service line connection, use of sanitary catch basin and tight construction supervision.