Contents

Introduction:
   What are CSOs
   Why are there CSOs?
   Where are King County CSOs?

Controlling CSOs
   How do we control CSOs?
   Transferring flow
   Increasing capacity
   Constructing local CSO treatment
     facilities
   Reducing stormwater entering the
     system

Reduction and Cost
   Requirements for CSO control
   How much have CSOs been reduced?
   What are CSO Control costs?

The CSO Program:
   CSO Projects
   Notification and Posting
   Sediment Management
   Water Quality Assessment
   Annual Report
   Program Updates
   Regional Wastewater Services Plan

Being a Good Neighbor

This page: Program Library

Glossary of Terms

A King County
Earth Legacy Program

2006-2007 (1.1MB)
2005-2006 (513KB)
2004-2005 (381KB)
2003-2004 (313KB)
2002-2003 (264KB)
2001-2002 (300KB)
2000-2001 (255KB)

1999-2000 (2.9MB)
1998-1999 (3.7MB)
1997-1998 (4.0MB)
1996-1997 (3.3MB)
1995-1996 (3.3MB)
1994-1995 (4.2MB)
1993-1994 (2.0MB)

1992-1993 (1.3MB)
1991-1992 (1.2MB)
1990-1991 (1.2MB)
1989-1990 (862KB)
1988-1989 (739KB)
1987-1988 (400KB)

The state Department of Ecology’s CSO regulation (WAC 173-245) (external link) and King County’s RWSP policies require WTD to submit a CSO plan update to Ecology that coincides with each NPDES permit renewal for the West Point Treatment Plant. Updates are intended to describe WTD’s progress on its CSO program to date, identify its program for the next 5 years, and provide a vehicle for making changes in the overall long-term CSO control program. WTD prepared such an update in 2000 (see below) when the West Point NPDES permit renewal was submitted to Ecology.

In addition to updates, the RWSP policies call for a CSO control program review to be done prior to the plan update that would occur as a part of the next NPDES permit renewal following the plan update and permit renewal in 2000. At the time the RWSP was prepared, the update and permit renewal were anticipated to be due in 2005. Ecology subsequently determined that the next NPDES permit renewal will be due in 2008.

The CSO program review is now completed—well ahead of the 2008 Ecology-required update and permit renewal—providing the King County Council and the Regional Water Quality Committee (RWQC) time to comment on or make any needed recommendations to modify the CSO program.

King County CSO Public Notification Feasibility Study, July 2007
Letter to Ecology
Complete document (1.8MB)

CSO Control Plan Review, April 2006
Table of Contents
Executive Summary
Complete document (1.5MB)

2000 CSO Control Plan Update, June 2000
Table of Contents (121KB)
Complete document (6.1MB) 

King County CSO 5-Year Update
Task 4.0, Development of Alternatives, December 1997
Table of Contents (548KB)
Executive Summary (525KB)
Complete document (43MB)

METRO CSO 5-Year Update
Task 5 Report, RWSP System Alternatives,
Supporting CSO Project Descriptions, August 1995
Table of Contents (118KB)
Complete document (21MB)

1995 CSO Control Update, February 1995
Table of contents (113KB)
Complete document (5.2MB)

1986-1991 CSO Control Plan Update, January 1992
Table of contents (59KB)
Complete document (1.7MB)

1988 CSO Control Plan, April 1988
Table of contents (89KB)
Complete document (4.3MB)

1986 Final Supplemental Plan for CSO Control: Plan for Secondary Treatment Facilities and CSO Control, Volume 3, July 1986
Table of contents (194KB)
Complete document (6.6MB)

This study was completed in 1998 with help from a large stakeholder group and the Water Environment Research Foundation (external link).

King County Combined Sewer Overflow Water Quality Assessment for the Duwamish River and Elliott Bay, February 1999
Table of Contents (Volume 1: Overview and Interpretation)
Complete document (Volumes 1-4)

Off-Site Facilities: An Overview of King County Pump and Regulator Stations, June 1999 (1MB)

1958 Metro Sewer Comprehensive Plan
King County residents voted in 1958 to build and operate a regional agency called the Municipality of Metropolitan Seattle, or Metro, to clean polluted waters of Lake Washington and Puget Sound. Since then, we have helped prevent water pollution and improve water quality while recycling natural resources. No longer called Metro, the wastewater utility is now a division in King County's Department of Natural Resources and Parks.

The Regional Wastewater Services Plan (RWSP) is the most recent update to the 1958 Plan and outlines a number of important projects and programs that King County will implement through 2030.

Programs

• CSO Control Program
• Community Relations
• Duwamish Waterway Programs
• Industrial Waste Program
• Inflow & Infiltration Program
• Local Hazardous Waste Program
• Marine Monitoring
• Regional Wastewater Services Plan
• Seattle-King County Public Health CSO Public Notification Program
• Trouble Call Program
• Wastewater Water Conservation Program
• West Point Treatment Plant

Projects

• CSO Water Quality Assessment
• Lower Duwamish Waterway Group
• Duwamish/Diagonal Sediment Remediation Project
• Conveyance System Improvements Project

Reducing Stormwater Into The Wastewater System

• Use a rain barrel to reduce stormwater into the wastewater system, save money on your water bills, and conserve water
• Disconnect and reroute roof and yard drains that run into the sewer system
• Stop Sewer Backups: How to Safeguard Your Home and the Environment by Disconnecting Downspouts
  (Water Environment Federation information)
• Reduce and eliminate inflow & infiltration

Keep Trash and Other Items Out of the Wastewater and Stormwater System

• If it's not biodegradable, put it in the trash can, not the toilet, or recycle it.
• Get rid of stuff you don't want or need -- recommended methods
• Reduce your use of materials with potential endocrine disrupting chemicals
• Fat-Free Sewers: How to Prevent Fats, Oils, and Greases from Damaging Your Home and the Environment
  (Water Environment Federation information)
• Alternatives to Household Hazardous Products
• Dispose of household hazardous waste properly
• Resources about practicing natural yard care
• Storm Drain Stenciling Project

Touring Treatment Plants and/or CSO Control Projects

• Treatment Plant Tours, CSO Control Project Tours

Miscellaneous Resources

• Conserve water at home
• Learn how to reduce household sewer odors
• Learn how to report sewer odors
• Stay informed about current wastewater treatment activities
• Report drainage and water quality problems (for areas in unincorporated King County )
• Apply for a Water Works grant to protect water quality
• Seattle Public Utilities Information (external links)
  • Tips to Prevent Sewer Backups
  • Tips to Prevent Health Problems from a Sewer Backup
• Resources for Teachers and Students
  • The Salmon Challenge Game (see how your decisions help or harm our environment and the salmon)
  • List of environmental resources for students and teachers
  • Natural Resources Kids Page
  • San Diego Wastewater Website for Kids (external link)

Older combined sewer
(pre-1950s)

Combined sewer
(post-1950s)

Separated sewer

CSO reduction graphic

CSO map

CSO phasing graphic

Regulator Station

Pump Station

Examples of King County CSO outfall locations

Norfolk CSO
(1992)

King Street CSO
(1992)

Brandon Street CSO
(1992)

Michigan Street CSO
(1992)

Denny Way CSO
(1992)

Denny Way CSO
(2004)

The outfall, pictured at left, was removed in 2003,
improving the Elliot Bay shoreline.

Denny Way
Regulator Station
(2004)

Green Roof at
Dexter Regulator Station
(2002)

King Street
Regulator Station
(2005)

Examples of King County CSO Treatment Facilities

Carkeek Park CSO
Treatment Facility
(1994)

Alki CSO
Treatment Facility
(2002)

Elliot West CSO
Treatment Facility
(2005)

Examples of King County Pump Stations
(in the combined sewer service area)

Henderson Street Pump Station
(2004)

West Seattle Pump Station
(1999)

Interurban Pump Station
(1996)