North Henderson Combined Sewer Overflow (CSO) Reduction

Aerial photo of tennis courts on top of storage tank in Seward Park.
New tennis courts were installed on top of a new 2.65-million-gallon storage tank in south Seward Park.

Project Description

Seattle Public Utilities (SPU) built two new underground storage facilities as part of the Henderson North Combined Sewer Overflow Reduction project. SPU constructed a 16,000-gallon storage pipe in 57th Avenue South near Martha Washington Park and a 2.65-million-gallon underground storage facility beneath Seward Park to reduce the frequency and volume of stormwater and untreated sewage that overflows into Lake Washington during heavy rain events.

Location

These projects were located in 57th Ave S near Martha Washington Park and in Seward Park.

Project Results

In addition to reducing combined sewer overflows (CSO) into Lake Washington, this project also included creative design elements and public amenities along the south shoreline of Seward Park such as:
This project also included creative design elements and public amenities along the south shoreline of Seward Park such as:

  • An enhanced shoreline with clear views of Lake Washington and Mount Rainier with improved natural aquatic habitat (trees installed on the shoreline were repurposed after being removed by the project);
  • An Americans with Disabilities Act (ADA)-compliant pedestrian promenade and pathway that connects to other park amenities;
  • An improved, ADA-compliant parking lot with wider spaces and a turnaround area;
  • New and improved tennis courts;
  • An odor control system which will treat air from both the new and existing CSO facilities; and
  • A replacement outfall pipe that will carry future overflows farther away from the shore.

Timeline

Construction was completed in spring 2017.