Background

Sewage and stormwater (runoff from roofs, streets, and sidewalks) from many older parts of the city, including areas within Delridge, combine into one network of pipes (a combined sewer system). In dry weather conditions, all flows in these pipes go to King County's wastewater treatment system (shown below).

Depicts the flow of sewer in dry weather, described in page text

During the heaviest rainstorms (shown below), combined sewers can fill to capacity and any excess of that combined mixture of stormwater (90%) and sewage (10%) can overflow to the nearest water body to prevent sewage from backing up into homes and streets. 

Depicts sewer flow when in heavy rain situations, as described in page text.

In Delridge, the nearest water body is Longfellow Creek. These combined sewer overflows, or CSOs, contain contaminants that can make people sick and harm fish, wildlife, and the environment.In some parts of the city, there are two pipe networks in the street: one to carry sewage (separated sewer systems) and another to carry stormwater runoff (the "drainage system"). Seattle's drainage system discharges stormwater directly to creeks, rivers, lakes, and Puget Sound. Although there is no sewage in stormwater, it still can carry harmful contaminants such as from street runoff that can also make people sick and harm fish, wildlife, and the environment. In some parts of Delridge, there is a drainage system that discharges to Longfellow Creek.

In order to improve the water quality in the creek, we are looking for ways to reduce the amount of water entering the creek during heavy rainstorms and how to make our combined sewer system and drainage systems more flexible and adaptable in response to changing weather patterns due to climate change.