Infiltration & Inflow Reduction Effectiveness From Private Property Rehabilitation

In 2007, the King County Wastewater Treatment Division (WTD) began a project to explore the feasibility of regional I/I reduction. Previous studies had identified the need for a peak-flow storage facility to prevent sanitary sewer overflows from the County’s regional conveyance system into Lake Washington. The objective of this Demonstration I/I Reduction Project was to remove enough I/I from the local wastewater collection system to eliminate the need for this storage facility, resulting in a net cost savings to the County. I/I reduction measures concentrated on the rehabilitation of sewer system components on private property, which were suspected to represent the major source of I/I in the system. The project included replacement of sewer laterals and side sewers on 300 private properties by pipe bursting. Modeling was performed to determine the effectiveness of the sewer rehabilitation effort. The project was successful in removing some peak I/I, but the results were less than expected in the lower part of the basin. Lessons learned from the project are included in the paper.