Program history

The King County Regional Infiltration and Inflow (I/I) Control Program was created in 1999 as part of the Regional Wastewater Services Plan (RWSP) to explore the feasibility of I/I control.

In response to the RWSP I/I Control Program policies, WTD staff, working in a consensus-based approach with local sewer agencies, conducted a comprehensive 6-year, $41 million I/I control study. The study began in 2000 and culminated with the Executive's recommendation for a regional I/I control program. The following work was completed as part of this study:

• Defined current levels of I/I for each local agency tributary to the regional system through extensive flow monitoring and modeling program (2001-2002).
• Selected and constructed 10 pilot projects in 12 local agency jurisdictions to demonstrate the effectiveness of collection system rehabilitation projects and to test various technologies and gain cost information (2003-2004).
• Developed final draft model standards, procedures, policies, and guidelines (October 2004) for use by local agencies to reduce I/I in their systems. These will remain draft pending completion of the recommended initial projects in 2013.
• Completed a thorough benefit-cost analysis to determine the cost-effectiveness of I/I reduction (November 2005).
• Developed a long-term regional I/I control plan, approved by the King County Council (May 2006).
• King County worked with the local sewer agencies to conduct an I/I reduction feasibility analysis and selected three initial I/I reduction project areas (2007-2009).

Next steps

During 2011 King County will construct an initial I/I reduction project in the Skyway Water & Sewer District service area (unincorporated King County). Selected I/I reduction projects in Bellevue and Issaquah were cancelled in early 2010 due to County budget limitations. The Skyway project will test the cost-effectiveness of I/I reduction on a scale large enough to offset the need for a larger conveyance or storage facility. The results of this initial project will be used to develop recommendations to the King County Council regarding long-term I/I reduction controls, including applicable changes to policy or code.