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King County Washington home

Environmental review

This page lists environmental documents prepared by the King County Wastewater Treatment Division that are currently available for public review and comment.

Documents currently available for public comment

MDCSO

Title of proposal: Mouth of Duwamish Wet Weather Facilities Program

Description of proposal: King County proposes to construct new infrastructure to control five combined sewer overflow (CSO) outfalls in the East and West Waterways of the Duwamish River and Elliott Bay. The proposal will improve water quality by reducing untreated overflows of combined sewage and stormwater during large storms. This work fulfills requirements of a consent decree the County has with the U.S. Environmental Protection Agency and the Washington State Department of Ecology. Under the consent decree, King County is legally obligated to complete construction by December 31, 2034.
The Mouth of Duwamish Wet Weather Facilities Program consists of two projects: the SODO Wet Weather Treatment Station (WWTS) Project and Chelan Wet Weather Storage Project. The SODO WWTS Project includes construction of a new wet weather treatment station in the SODO neighborhood and a new outfall in the East Waterway, along with associated conveyance and supporting infrastructure. The Chelan Wet Weather Storage Project includes construction of a new storage tank in the Delridge neighborhood and related conveyance facilities.

Location of proposal, including street address, if any: The program is located within Seattle’s SODO, Pioneer Square, and Delridge neighborhoods. The program components will be located on current WTD owned parcels, Seattle Department of Transportation Right-of-Way, and private property. Parcels applicable to the program: 7666207503, 7666207496, 7666207491, 7666207461, 7666207462, 7666206715, 7666206710, 7666207697, 7666207905, 7666703464, 7666703966, 7666703967. Additional parcels for project elements that have not yet been sited will be added as design progresses.

Issue date: June 26, 2026

Comment deadline: July 13, 2026

Submit comments via email to: WTDSEPA@kingcounty.gov; or via postal mail to:

Jacob Sheppard, Supervisor, Environmental Planning, King County Wastewater Treatment Division, 201 South Jackson Street, MS KSC-NR-6200, Seattle, WA 98104-3855.

Download documents: Determination of Nonsignificance (DNS) and Environmental Checklist.

Frequently asked questions

The listed documents are mainly threshold determinations and checklists prepared under the Washington State Environmental Policy Act (SEPA statute, RCW 43.21C; SEPA Rules, WAC 197-11). Other environmental documents prepared by the Wastewater Treatment Division, such as documents prepared under the National Environmental Policy Act (NEPA), may also be listed.

Local, state and federal regulations mandate the ways in which agencies must notify the public that environmental documents are available for public comment. These may include mailings, signs and/or newspaper notices. The Wastewater Treatment Division typically makes the documents available in local libraries and upon request. This web page is another way in which the division provides notice and copies of these documents.

You may view and download an electronic copy of each listed document by clicking on the associated link. Information on how to provide comments on each document listed below is included in the document. 

Yes. Please refer to the SEPA appeal process.