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Learn more about the Brightwater Treatment Plant and Brightwater Center.

Completed – Fall 2012

In response to increased growth in our region, King County has built a new $1.86 billion regional wastewater treatment system called Brightwater to serve the northern portion of the King County service areaTreatment plant operations began in September 2011. The conveyance system and outfall began full operations in fall 2012.

Map of Brightwater project facilitiesBrightwater treatment system  . View more detailed 11x17 inches map  .

The new facilities include:

  • The Brightwater Wastewater Treatment Plant is located in unincorporated Snohomish County, north of Woodinville. The plant is designed to have the capacity to treat an average of 36 million gallons of wastewater per day (mgd). By 2040, treatment capacity could be expanded to 54 million mgd.
  • The conveyance system is the tunnels, pipes, and other facilities that carry wastewater to and from the treatment plant. The Brightwater system includes 13 miles of pipeline built in underground tunnels, shallower connector pipes, and an influent pump station to send wastewater to the plant.
  • The marine outfall consists of twin, 5-foot-diameter pipes with a diffuser at the end where highly treated wastewater from the Brightwater Treatment Plant is discharged into Puget Sound. The mile-long, 600-foot-deep outfall extends off of Point Wells.
Brightwater Treatment Plant opening (September 24, 2011) from King County DNRP on Vimeo 

Background – siting the Brightwater facilities

Beginning in the summer of 2000, the County began searching for and analyzing sites. In May, 2001 the King County Council selected six sites and eight marine outfall sites for further evaluated as “systems” (including a plant site, conveyance system and outfall).

In June 2001, the county began a second round of evaluation. Based on this, the County Council selected two systems–including conveyance options and four marine outfall zones–to continue on into the environmental review process.

King County conducted a formal environmental review of the Brightwater project under the State Environmental Policy Act (SEPA). On November 19, 2003, a Final Environmental Impact Statement (Final EIS) was issued for this project.

Project siting decision

On December 1, 2003, the King County Executive made a decision on the location for the Brightwater treatment system  .

On July 27, 2005 the King County Executive reaffirmed his earlier selection of the Route 9 - 195th St system alternative for the Brightwater project. To learn more, download the Regional Wastewater Services Plan: summary of the Executive's process to update the Brightwater system siting decision, July 2005  .

In December 2005, King County completed a systemwide mitigation package .

Project videos

The following links point to DNRP Vimeo  videos.

operations phase

24 hour emergency and odor reporting:

Contact Brightwater Treatment Plant at  206-263-9500.

Marine outfall (off of Point Wells)

Conveyance facilities (pipelines and portals)

Treatment plant (near Woodinville, WA)

Reclaimed water system

North mitigation area (north end of treatment plant site)

Environmental education center (north end of treatment plant site)

Marine restoration (at the marine outfall) 

Video: First flow of clean test water to come into the Brightwater Plant from the Influent Pump Station in Bothell, 2.8 miles away! (May 2011)Brightwater plant test (May 2011)
Video length: 17 seconds

Video: installation of membrane bioreactor filters (MBRs) at the treatment plant (April 2011).Installation of membrane bioreactor filters (MBRs) at the treatment plant (April 2011)
Video length: 2 minutes, 32 seconds

Video: Earth Week at Brightwater Center (April 2011) Earth week at Brightwater Center (April 2011)
Video length: 2 minutes, 4 seconds

Smooth sailing for Brightwater outfall pipelines (September 2008)Smooth sailing for Brightwater outfall pipelines (September 2008)
Part 1 – the first outfall pipeline was submerged on September 10, 2008
Part 2 – the second outfall pipeline was submerged on September 12, 2008

Brightwater treatment plant introduces tunneling equipment (September 2007)Brightwater Treatment Plant introduces tunneling equipment (September 2007)
Video length: 1 minute, 46 seconds

Brightwater habitat restoration tours, April 2007Take a tour of the Brightwater habitat restoration (April 2007)
Video length: 4 minute, 16 seconds

Background – environmental review

King County conducted a formal environmental review of the Brightwater project under the State Environmental Policy Act (SEPA). This review evaluated wastewater system alternatives in an environmental impact statement (EIS).

The purpose of an EIS is to inform decision makers and the public about the probable significant adverse environmental impacts and potential mitigation measures for the proposed project.


  • On November 19, 2003 the county issued a Final Environmental Impact Statement (Final EIS) for this project. The county also issued five addenda to the EIS to provide additional information or analysis that does not substantially change the analysis of significant impacts and alternatives in the Final EIS.
  • A Draft Supplemental EIS was issued on April 11, 2005. This provided new information and its relationship to the Brightwater Treatment Plant site and evaluated the significant adverse environmental impacts that could result if an earthquake were to occur on the Southern Whidbey Island Fault and damage treatment plant facilities. A Final Supplemental EIS was issued July 19, 2005, and includes comments received and responses to these comments.
  • On July 27, 2005 the King County Executive reaffirmed the county's choice of the Route 9 treatment plant and 195th St conveyance alternative for the Brightwater project  . A notice of action was issued for this action on August 11, 2005.
  • On October 2, 2006 the Court of Appeals issued a decision agreeing with King County regarding preparation of a Supplemental Environmental Impact Statement (SEIS). The Court's decision directed the superior court to prohibit the hearing examiner from conducting an appeal of the adequacy of the SEIS that was filed on the project.

Final EIS

King County's Department of Natural Resources has prepared this Final Environmental Impact Statement (Final EIS) on the Brightwater Regional Wastewater Treatment System. The Final EIS provides information and evaluation of the probable significant adverse environmental impacts of the Brightwater proposal and identify alternatives and reasonable mitigation measures.

What is included in the Final EIS

The first three chapters (included in Volume 1) contain a project description, comparison of alternatives, background, and summary of impacts and mitigation measures. The comparison of alternatives highlights key environmental issues and options. Impact comparison tables are located in Chapter 3.

Additional chapters 4-17 (in Volumes 2 and 3) sets forth this analysis in greater detail. Following Chapter 17, you will find a glossary, distribution list, and the summary of the Brightwater Summer 2003 technical seminars. Five addenda to the Final EIS have also been issued.

The remaining volumes include appendices that provide background and technical information for corresponding chapters in the Final EIS (in Volumes 4-10), Draft EIS comments and responses (in Volumes 11-15) and comments from the Summer 2003 technical seminars (Volume 16).

You can download and view documents (PDF files) using a PDF Reader.

Final Environmental Impact Statement (EIS) Table of contents

Appendices for chapter 2, background

Appendices for chapter 3, description and comparison of alternatives

Appendices for chapter 4, Earth

Appendices for chapter 5, air

Appendices for chapter 6, water resources

Appendices for chapter 7, plants, animals, and wetlands

Appendices for chapter 10, noise and vibration

Appendices for chapter 11, land and shoreline use

Appendices for chapter 13, light and glare

Appendices for chapter 15, cultural resources

Appendices for chapter 16, transportation

Addendum no. 5 and final supplemental EIS addendum no. 2, issued January 3, 2007 (60 KB)

This addendum reports on the results of seismic trenching on the Brightwater Treatment Plant site in the summer of 2006 and the approach to seismic design on the site. The report and memo referenced in the addendum are available here.

Addendum no. 4, issued September 1, 2004 (317 KB)

Provides additional information on and/or evaluation of the impacts of constructing and operating:

  • The influent pump station at portal 41;
  • facilities along the conveyance corridor; and
  • the safety relief point at a location 200 ft west of the location identified in the final EIS.

Addendum no. 3, issued April 30, 2004 (3.9 MB)

Provides the following:

  • an updated evaluation of aeromagnetic and LiDAR imagery for the postulated onshore extension of the South Whidbey Island fault
  • a review of boring data and a seismic refraction survey at the Route 9 site
  • an analysis of ground motion studies at the Route 9 site
  • a description of geotechnical data that will be used for design of the conveyance system and outfall
  • additional discussion of the final EIS worst-case analysis of impacts and mitigation measures associated with major seismic events

Addendum no. 2, issued April 2, 2004. (3.7 MB KB)

Provides the following:

  • Identifies selected portal sites
  • Provides information and analysis of the impacts of using trucks, barge, or rail for transporting excavated materials away from the portal 19 site at the Chevron-Texaco Richmond Beach asphalt terminal.
  • Describes and analyzes the impacts of a proposed temporary construction access road at the southern end of the Route 9 site and installation of a traffic signal at the SR-9/SR-522 Westbound ramp intersection to reduce construction-related traffic along SR-9 north of SR-522
  • Provides more information and analysis of impacts of demolition and construction on the Route 9 site, particularly in relation to the StockPot Culinary campus

Addendum 1, issued January 27, 2004. (288 KB)

Provides the following:

  • an updated analysis of traffic impacts and mitigation measures using alternative assumptions related to background traffic growth rates for the eastern portion of the project area
  • additional information about potential improvements to and use of the existing barge dock at the Chevron Richmond Beach asphalt terminal for transporting materials and spoils during construction of the conveyance pipeline and the marine outfall at Point Wells

King County prepared this final supplemental Environmental Impact Statement (final Supplemental EIS) on the Brightwater regional wastewater treatment system. The final supplemental EIS is a supplement to the final EIS issued in November 2003.

A 16-page summary (2 MG) of the final supplemental EIS is also available.

The final supplemental EIS includes:

  • comments made on the draft supplemental EIS and responses to comments
  • changes made to pages in the draft supplemental EIS, organized by chapter and appendix
  • updated cover letter, foreword, fact sheet, acronyms and abbreviations, glossary, and distribution list; and errata sheet
  • the two-volume draft supplemental EIS, issued April 11, 2005

Final supplemental EIS

Cover letter (32KB)

Foreword (17KB)

Fact sheet (67KB)

Acronyms and abbreviations (19KB)

Table of contents (20KB)

Summary responses to comments (220KB)

Individual responses to comments (22.4MG)
    Government agencies, organizations, individuals

Changes in the supplemental EIS text made in response to comments (5.6MG)
       Chapter 1
       Chapter 2
       Chapter 3
       Chapter 4
       Chapter 5
       Appendix G (added)

Glossary (84KB)

Distribution List (28KB)

Errata (28KB)

The May 4, 2005, public hearing transcript (56KB)

Draft supplemental EIS, issued April 11, 2005

Cover letter (26KB)

Foreword (44KB)

Fact sheet (60KB)

Acronyms (15KB)

Table of contents, list of tables and figures (37KB)

Chapter 1 – Introduction (1.74MB)

Chapter 2 – Seismic background and context (1.3MB)

Chapter 3 – Design of the Brightwater Treatment Plant (2.22MB)

Chapter 4 – Worst-case earthquake scenarios assumed in the impacts analysis (1.41MB)

Chapter 5 – Environmental impacts if a major earthquake were to damage Brightwater facilities and mitigation of impacts (1.0MB)

Scenario tables (79KB)

Glossary (84KB)

Distribution list (31KB)

Draft supplemental EIS appendices (note large file sizes)

Appendix A – Surface-fault-rupture hazard evaluation (14.2MB)

Appendix B – Revised probabilistic seismic hazard analyses (3.8MB)

Appendix C – Building code regulations and seismic studies used in the structural design of the Brightwater facilities (108KB)

Appendix D – Emergency overflow surface water impacts analysis (343KB)

Appendix E – Analysis of flooding and water quality effects in Little Bear Creek following a major earthquake (2.1MB)

Appendix F – Brightwater SEPA supplement groundwater evaluation (5.8MB)

Note: though not issued as part of the draft supplemental EIS, an appendix G has been added – see above under: "Changes in the supplemental EIS text made in response to comments"

Seismic and geologic studies

Treatment plant – approach to seismic design. CH2M Hill, Brown and Caldwell, Mithun. Oct. 9, 2006 (235 KB)

Note: this memo has been updated and the updated version, above, was posted on this web site on Jan. 8, 2007. Changes have been made on the following pages:

  • Pg 1: New engineering stamps and signatures have been provided
  • Pg 5: "Snohomish PUD substation" has been added to seismic use group III in table 1
  • Pg 6: The first sentence regarding the peak level of ground shaking has been revised.

In addition, a footer has been added to the updated document. Otherwise, the remainder of the document is unchanged.

This report and memo are referenced in Brightwater final EIS addendum no. 5 and final supplemental EIS addendum no. 2, issued January 3, 2007

Chemical building seismic trenches, Brightwater Wastewater Treatment Plant site, Oct. 19, 2006, pages 1-27 (225 KB)

Report figures, pages 28-59 (5.5 MB)

Appendix A - Trenching investigations of the proposed buildings (3.4 MB)

Appendix B - Radiocarbon dating results (75 KB)

Appendix C - Liquefaction article (4.5 MB)

Appendix D - Comments relevant to USGS site visit report, July 6, 2006 (102 KB)

Appendix E - Comments relevant to Dr. Yeats’ e-mail letter, transmitted July 12, 2006 (38 KB)

Appendix F - Responses to report of August 21, 2006 by Earth Consultants International (411 KB)