Simple retrofits, like adjusting the height of the weir shown in this photo, provide cost-effective ways to reduce CSOs.


Seattle also gains additional storage capacity by retrofitting existing facilities. The Retrofit Program helps to reduce the frequency and volume of CSOs through relatively low-cost, simple fixes to the system, such as adjusting the height of the gates to provide small amounts of additional storage.

Since 2003, more than 35 such retrofits have been performed to better control CSOs throughout the city.

About 60 retrofit projects are on the drawing board, many of which have also been identified as part of the CSO Long-term Control Plan Monitoring Program, which has been collecting data for more than two years to create models that will be used to determine how best to control CSOs in each basin. Construction projects are planned or in development at the following locations:

Windermere: Retrofit an existing flow control chamber and install new monitoring sensors on NE Ambleside Road, west of NE Penrith Road.

These retrofits include work inside existing structures, installing new sewer/drain lines and/or relocating structures:

West Seattle - Fauntleroy Way SW & SW Brace Point Dr.

North Union Bay - NE 41st St from 38th Ave NE to the west and 40th Ave NE and NE 52nd

South Henderson - Rainier Ave. S. and S. Cooper St.

In addition, improved operations and maintenance for existing facilities will also provide some affordable ways to optimize system performance. For example, replacing or lining defective pipes can reduce the volume of polluted runoff from leaks. Real-time controls are being installed so that adjustments can be made more quickly when needed during large storms.

Delridge: Delridge Way SW & SW Orchard St. (Site 168)
22nd Ave. SW & SW Henderson St. (Site 169)

Retrofit two passively controlled systems to allow better monitoring and flow control, reducing the frequency of Combined Sewer Overflows (CSOs) into Longfellow Creek.

Contact the Retrofit Team.