Regional Infiltration and Inflow Control Program

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

The purpose of the program is to reduce the amount of peak wet weather flow entering the County's wastewater conveyance system when it is cost-effective to do so. Reduction of I/I in the system has the potential to lower the risk of sanitary sewer overflows and decrease the costs of conveying and treating wastewater.

Work completed to date

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 culminates 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.
• 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.
• Developed model standards, procedures, policies, and guidelines for use by local agencies to reduce I/I in their systems. These will remain draft pending completion of the
  recommended initial projects.
• Completed a thorough benefit-cost analysis to determine the cost-effectiveness of I/I reduction.
• Developed a long-term regional I/I control plan for review and approval by the King County Council.

Next Steps

The King County Council will be reviewing the program recommendations in 2006.

More Information

• For questions about the I/I Control Program Web site, please contact Maryann Petrocelli at 206-263-7321 or maryann.petrocelli@kingcounty.gov.
• Archived news releases.

Department of Natural Resources and Parks
Wastewater Treatment Division
201 S. Jackson St.
Seattle, WA 98104-3855
Fax: 206-684-1278

Updated: Jan. 15, 2008

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