Georgetown Wet Weather Treatment Station construction update

December 2018 Project Update

King County's Wastewater Treatment Division (WTD) is building a new wet weather treatment station in Georgetown at the corner of Fourth Avenue South and South Michigan Street. As part of the Wet Weather Treatment Station project, WTD is also building a new outfall structure under the First Avenue South Bridge and connecting pipes from the station to the outfall. 2018 was an exciting year with construction starting at all three project areas. Below we have shared a few highlights for each site from the past year.

In March 2018, King County celebrated the start of construction at a groundbreaking ceremony with Executive Dow Constantine, Department of Natural Resources and Parks Director Christie True, WTD Director Mark Isaacson, and Bardow Lewis of Suquamish Tribe. Since then, crews have worked on the regulator structure, pump station and piping around the site.

Crews began construction at the treatment station site by installing four-foot wide concrete cylinders, also known as secant piles, in the ground. Secant piles lock together to create a structurally stable ring.

 

Crews also used a vibratory hammer (left) to install steel sheet piles to hold back water and soil while they excavated additional supporting structures. Rebar (right) is sized and placed prior to pouring concrete to help reinforce the structures on the treatment site.

Next year, we are looking forward to continuing work on the regulator structure, influent pump station and other supporting structures.

Outfall pipes

Crews began construction on the outfall structure located under the First Avenue Bridge in July 2018. They have continued to make progress over the past couple of months by working along the Duwamish River to build the drop structure and install the pipes.

The trestle (left) will continue to be installed, eventually moving into the Duwamish River. It will be used to hold the crane and excavator needed for pipe installation. To protect the Duwamish River during construction, crews installed a flexible sediment control barrier (right), also known as a turbidity curtain, to prevent silt and sediment from entering the waterway.

Crews poured concrete to create the foundation of the outfall 's drop structure which will be used to control the release of treated water into the Duwamish River.

Conveyance pipes

In early November, crews began preparing the site near Evergreen Tractor by South Michigan Street for the conveyance construction. As part of the site preparation work, existing structures in the area were removed and sheet piles will be installed. There is no work planned in the road for this first phase of work.

Crews will use shoring boxes (left) during conveyance construction to secure excavation. Sediment and erosion control best management practices (BMPs), shown on the right, will be used throughout construction to control dust and keep dirt contained on site.

60-inch diameter pipe is being delivered and stored on the construction site prior to installation.

For more information about the project, visit: https://www.kingcounty.gov/GeorgetownWWTS