How Bad Is It? Assessing Peak Inflow and Infiltration in King County's Service Area

King County is embarking on an extensive program to assess inflow and infiltration (I⊘I) in each of 34 component agencies in the county's service area. The program will include rainfall and flow monitoring, computer modeling, economic analyses, field investigations, and pilot projects to ascertain if it is cost effective to remove I⊘I from the system. Representatives from each of the component agencies are involved in providing input to the program such that a regional consensus can be formed around a reasonable solution to the I⊘I problem.I⊘I is the major driver in the need for 770 million dollars of new conveyance facilities over the next 30 years. The investment in the I⊘I Program is being made in the hopes that tens or hundreds of millions of dollars can be saved if an effective I⊘I program is implemented. The assessment might also find that it is not cost effective to remove I⊘I. A preliminary assessment in 1995 indicated that an expenditure of 100M in sewer rehabilitation could result in a decrease of 300M in conveyance facilities. The goal of this regional assessment is to develop detailed information about the location of I⊘I sources and potential cost-effective improvements to remove or reduce critical sources of I⊘I. At least 10 pilot projects are to be conducted to determine how effective I⊘I reduction efforts might be.Computer modeling of I⊘I into the sewer system is a core effort in the County's I⊘I Program and will provide the information and analysis needed to determine the types of I⊘I in the system, and the benefits that might be achieved if aggressive I⊘I control were to be implemented. King County and consultant staff are well underway in performing the needed modeling work for the project, which is scheduled for completion in 2004. A computer model search and evaluation was conducted, a model has been selected and purchased, model basins have been defined, rainfall and flows have been measured, and some model basins have been calibrated. This paper presents the information that has been gained so far through the modeling effort and how the modeling information will be used in King County's I⊘I Program.