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Infiltration and Inflow Control

King County, Washington

For more information about the Regional Infiltration and Inflow Control Program, please contact Steve Tolzman.

Wastewater Treatment Division
King Street Center
Suite 0505
201 South Jackson Street
Seattle, WA 98104

Get Directions to our office location in Seattle, Washington

Fixing infiltration and inflow (I/I)

Once an I/I problem has been identified, there are many methods and technologies available to reduce I/I. One primary method focuses on fixing the broken pipes, manholes, and joint connections. Another focuses on reducing the amount of I/I that enters the sewer system from storm events by disconnecting roof drain downspouts and other building or yard drains that may be directly connected to the sewer.

Trenchless technologies

Construction Equipment
Pipe bursting of private side sewer line.

Trenchless technology pipe repair methods may include pipe bursting, or cured-in-place pipe (CIPP). Pipe bursting is a technique that pulls a hardened steel breaker head through the old pipe, breaking it up, and replacing it with a new pipe all in one process.

CIPP repair involves pulling a resin-saturated liner through a damaged pipe which is then cured with steam or hot water to form a tight-fitting, jointless replacement pipe. Trenchless repair methods require less digging than traditional “dig and replace” repair methods and minimize damage to yards and landscaping.

Stormwater disconnections

Stormwater connections such as roof drain downspouts, yard drains, and sump pumps may be disconnected from the sewer system and redirected to a separate stormwater system.


Cutting Down SpoutRemoving Down SpoutCapping Down SpoutRedirecting Down Spout
Disconnecting a downspout consists of cutting the downspout, capping the drainage line and redirecting the flow.