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Regional Infiltration and Inflow Control Program

Regional Infiltration and Inflow Control Program

Reducing infiltration and inflow (I/I), which consists of stormwater and groundwater entering a sanitary sewer system, maintains pipe capacity for sewage in the County’s wastewater system. Maintaining capacity for sewage helps prevent overflows and reduces the need for capital projects to add sewer system capacity. King County is engaged in a long-term program, in collaboration with local wastewater agencies, to reduce I/I when cost effective to do so in the separated sewer system.

December 2022 Update

Side Sewer Maintenance Mailer, December 2022

King County recently developed an educational mailer for MWPAAC agencies to distribute to their residents. The mailer describes components of a side sewer, private property source disconnection, and side sewer maintenance best practices. The mailer is available in English as well as 11 other languages. MWPAAC agencies have the option to add their logo to the mailer before distributing it to their residents as well as posting to websites or other online platforms. The mailer was developed using guidance from the Side Sewer Best Management Practices (BMP) Toolkit.

The King County Wastewater Treatment Division (WTD) serves 34 local wastewater agencies in the regional service area. With the exception of the portions of the City of Seattle that have combined sewers, sewers in the regional wastewater system are designed to convey only wastewater.

However, many of these "separated" sewers also convey groundwater and stormwater that enters through leaky pipes, improper storm drain connections, and other means.

Learn more:

Contact your local sewer service provider for specific information about the sewer system in your neighborhood.

Nicole Smith
Capital Project Manager