Combined sewer overflows

How do we reduce overflows?

A Washington regulation (Chapter 173-245 WAC) requires communities to reduce the frequency of untreated combined sewer overflows. They are required to reduce overflow incidents to no more than an average of one discharge per year, per outfall.

Overflows are a problem

Without controls over combined sewer overflows (CSOs), large quantities of raw sewage can be released into lakes, rivers, and Puget Sound. Contaminants in CSOs can include pathogens, oxygen-consuming pollutants, solids, nutrients, and toxics — all of which can harm people, fish, and wildlife.

Our role in preventing CSOs

We target high priority pollution sources to protect public health. We use permits — and legal orders — to implement state and federal requirements for communities to control their overflows. The permits and orders often include schedules for when communities must complete control projects. 

If communities violate the conditions in their permits or orders, they may face penalties or other enforcement.

Community plans to control CSOs

We review and approve planning and engineering documents to ensure proposed wastewater projects comply with water quality laws. Our oversite of CSO communities includes reviewing the plans they develop to control their CSOs. Those plans can propose a variety of approaches to achieve control.

To control CSOs, they may:

• Separate sewer and stormwater collection.
• Construct large tunnels and tanks to store and then treat combined flows after storm events.
• Provide facilities that operate during high flows.
  • These facilities typically provide primary treatment, disinfection, and screening to remove large solids.
  • They must meet technology-based and water quality-based pollution limits in permits.
• Implement a green stormwater infrastructure. 
  • They can create roadside rain gardens, permeable pavement, and downspout-to-ground disconnects that reduce or eliminate the flow of stormwater into the combined sewer.

Communities with combined sewer overflows

CSO community	Date system expected to reach control	Number of CSO outfalls	Compliance documents			PARIS (permit database) summary page
Anacortes	Under control	2	Permit WA0020257	Fact Sheet		Anacortes Wastewater Treatment Plant
Bellingham	Under control	1	Permit WA0023744	Fact Sheet		Bellingham Sewage Treatment Plant
Bremerton	Under control	15	Permit WA0029289	Fact Sheet		Bremerton Sewage Treatment Plant
Everett	2027	13	Permit WA0024490	Fact Sheet	Order 11638	Everett Sewage Treatment Plant
King County	2030	38	Permit WA0029181	Fact Sheet	Consent Decree	King County West Point Wastewater Treatment Plant
LOTT	Under Control	1	Permit WA0037061	Fact Sheet (2005)	Fact Sheet Addendum (2011)	LOTT Wastewater Treatment Plant (Lacey, Olympia, Tumwater, Thurston Co.)
Mount Vernon	2015	2	Permit WA0024074	Fact Sheet		Mt. Vernon Wastewater Treatment Plant
Port Angeles	Under Control	3	Permit WA0023973	Fact Sheet		Port Angeles Sewage Treatment Plant
Seattle	2025 for all but 6 outfalls, 2030 for remaining outfalls	85	Permit WA0031682	Fact Sheet	Consent Decree	Seattle Combined Sewer Overflow projects
Snohomish	Under Control	2	Permit WA0029548	Fact Sheet		Snohomish Sewage Treatment Plant
Spokane	2017	20	Permit WA0024473	Fact Sheet		Spokane Riverside Park Water Reclamation Facility

Largest CSOs in the state: King County and Seattle

King County and the City of Seattle own and operate the two largest combined sewer systems in the state. The systems operated by them contain nearly 70 percent of the permitted CSO outfalls in the state.

Both local governments control different portions of a complex, interconnected system. Since CSO controls put in by one agency can impact the other’s system, both agencies must work together to solve shared problems. Given the size and complexity of the projects both agencies must complete, we recognize that it will take both agencies more time to control all of their outfalls.

Agreement to control overflows by 2025, 2030

We joined with EPA to negotiate separate federal agreements (consent decrees) with King County and the City of Seattle in July 2013. In those agreements, both King County and Seattle are scheduled to have their overflows mostly controlled by 2025.

The agreements generally:

• Set schedules for completing CSO control projects.
• Set requirements for sanitary sewer overflows.
• Set requirements for compliance with the county’s and city’s National Pollutant Discharge Elimination System (NPDES) permits.
• Set stipulated penalties for violations of the consent decrees and for certain NPDES permit violations.

A link to each agreement (called a consent decree) can be found in the summary table above.

Seattle prioritizing stormwater projects

Seattle’s agreement allowed them to defer completing projects to control six of their CSO outfalls until 2030 in exchange for completing high-priority stormwater projects by 2025. The city showed that the stormwater projects would provide a greater environmental benefit to the region than the CSO projects. 

Where does the money go?

Stipulated penalties are set in the consent decrees for violating the agreements. Penalties are based on the type of violation. These stipulated penalties are paid to both us and EPA.

We receive half of each penalty and deposit the money into the state’s Coastal Protection Fund. This fund pays for local projects throughout the state that improve water quality or enhance fish and wildlife habitat.  

King County stipulated penalties

King County’s consent decree requires them to complete all of the control projects identified in their 2012 CSO Control Plan by 2030. For more information about a specific penalty, see click the link to the demand letter in the table below.

Timeframe covered	Date of demand letter	Number of violations in penalty	Total amount of stipulated penalty	Amount paid
July 3, 2013 to March 31, 2013	Sept. 3, 2015 Letter	6	$12,000	$12,000
April 1, 2014 to Dec. 31, 2014	Dec. 1, 2015 Letter	7	$15,000	$15,000
Jan. 15, 2015 to Dec. 31, 2015	Nov. 21, 2016 Letter	23	$63,500	$63,500
Jan. 1, 2016 to March 31, 2017	Aug. 3, 2018 Letter	32	$100,500	$100,500
April 1, 2017 to Dec. 31, 2018	Nov. 4, 2019 Letter	20	$105,500	$105,500
Jan. 1, 2019 to June 3, 2020	Dec. 16, 2020 Letter	3	$14,000	$14,000

City of Seattle stipulated penalties

Seattle developed a plan in 2015 and is required to control all of its outfalls by 2025 except for 6 outfalls that will be controlled by 2030. For more information about a specific penalty, see click the link to the demand letter in the table below.

Timeframe covered	Date of demand letter	Number of violations in penalty	Total amount of stipulated penalty	Amount paid
July 3, 2013 to March 31, 2013	Feb. 9, 2015 Letter	2	$5,000	$5,000
April 1, 2014 to Dec. 31, 2014	Nov. 2, 2015 Letter	4	$16,500	$16,500
Jan. 15, 201 to Dec. 31, 2015	Nov. 21, 2016 Letter	10	$33,500	$33,500
Jan. 1, 2016 to March 31, 2016	May 27, 2017 Letter	3	$6,000	$6,000
April 1, 2016 to June 30, 2016	May 27, 2017 Letter	2	$15,000	$15,000
July 1, 2016 to Sept. 30, 2016	May 27, 2017 Letter	1	$1,000	$1,000
Oct. 1, 2016 to Dec. 31, 2016	May 27, 2017 Letter	1	$2,500	$2,500
Jan. 1, 2017 March 31, 2017	May 27, 2017 Letter	1	$2,500	$2,500
April 1, 2017 to Dec. 31, 2018	May 6, 2019 Letter	4	$8,500	$8,500
Jan. 1, 2019 to June 3, 2020	Dec. 12, 2020 Letter	9	$32,500	$32,500