Screenings improvement

April 2012 Update: view project animation.

Why does King County need to do this project?

The Influent Screenings Improvement Project addresses the need under current 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. The West Point Treatment Plant currently has 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 now not only means King County will meet new screening requirements, but also replaces an ageing facility that is reaching the end of its service life. The existing screens were installed when West Point Treatment Plant was upgraded to secondary treatment in the 1990’s, almost 20 years ago.

Project elements

To meet the updated screening requirements, King County will install new bar screens in the existing operating building and construct 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.

King County will install new bar screens in the existing operating building and construct a new building adjacent to the existing operating building to process the additional screened material. Source: Project criteria, City of Seattle Council Conditional Use Permit Application.

What you can expect

King County is working to design a facility that will provide safe and reliable operations and meet current regulations. The following are questions Discovery Park visitors and the community members may ask about facility design, construction, and operations.

Will construction affect park use?

• There will be construction traffic to haul materials and get workers to and from the site
• The elevation change, vegetation, and retaining wall along the east perimeter of the site will help screen out short-term disruptions to park users from noise due to construction activities

What will people see after the new building is constructed? 

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

• The proposed building is about 3,000 feet from the nearest residence
• The site will be partially screened from the south by the administration building 
• Views into the Treatment Plant are currently obscured by a berm planted with native vegetation 
• The height of the new building will be consistent with the height of existing buildings within the vicinity of the project area
• Exterior lighting design and placement will not result in increased glare from the site

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.

 
The new screenings process will improve the product from the current process (left), resulting in a cleaner, drier, more compact product (right).

Will the new facility need additional odor control?

The new facility will use the same type of odor control system as the existing 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 will result in a cleaner product for transport, reducing the potential for nuisance odors.

Schedule

Environmental documents

• West Point Influent Screenings Improvement Project  Determination of Nonsignificance and Environmental checklist, October 2011