Skip to main content

Screenings improvement - West Point Treatment Plant

Completed – Spring 2015

Why did King County need to do this project?

Construction on the Influent Screenings Improvement Project began spring 2013 and was completed spring 2015. This project addressed updated Washington State biosolids regulations to remove inert objects (trash and plastics) from solids destined for fertilizer use on farms and managed forests. These inert objects are transported for landfill disposal after removal. The regulations require treatment plants to screen these objects from the wastewater stream with 3/8-inch or finer bar screens before treatment and send this material to landfills. Previously, the West Point Treatment Plant had 5/8-inch screens.

The new Washington State Department of Ecology biosolids management regulations are outlined under Washington Administrative Code (WAC) 173-308-205.

Building this project not only means King County meets new screening requirements, but also replaces an aging facility that was reaching the end of its service life. The previous screens were installed when West Point Treatment Plant was upgraded to secondary treatment in the 1990’s, almost 20 years ago.

Project elements

King County installed new bar screens in the existing operating building and constructed a new building adjacent to the existing operating building to process the additional screened material. This project affords an opportunity to use updated solids processing technologies, including washing and compaction processes that will produce a significantly cleaner and drier product.


Animations like this one are generated early in project design and used to provide operations staff with a virtual walk through the facility and equipment layout. Staff can understand the facility design from a user’s standpoint and provide feedback to the design team. The virtual tour also helps the design team describe the project to the community.

WTD West Point Influent Screenings Improvement Project – 3D animation at 30% design from King County DNRP on Vimeo.

What do people see now that the new building is constructed?

The new screenings handling building is not noticeable by Discovery Park neighbors and users.


The screenings building addition blends in to existing buildings at West Point Treatment Plant

Will there be more truck traffic in Discovery Park once the screenings facility is in operation?

King County expects an actual reduction in truck trips through Discovery Park after the new facility is operational. While finer screens will result more inert objects being screened, processed and transported, the product will be drier and more compact than the current product. In addition, by removing more inert objects from the solids, fewer trips will be required to transport usable biosolids. Reducing truck trips not only benefits park users, but also affords energy savings.

Will the new facility need additional odor control?

The new facility uses the same type of odor control system as the previous facility. Air from the screenings facility will continue to be ventilated from the buildings and conveyed to air scrubbers before release to the atmosphere. Practices such as keeping doors closed and covering solids will be maintained. The washing process included in this project results in a cleaner product for transport, reducing the potential for nuisance odors

Screenings handling building