Sammamish Plateau Water has temporarily paused new sewer
connections in key areas with limited sewer capacity.

Affected sewer basins include: Northeast Plateau, Beaver Dam, Inglewood East, Tiburon, North Lake Sammamish, and Central Lake Sammamish (see map links to right).

For more information on this sewer moratorium, click here.

Sewer Moratorium - Frequently Asked Questions (PDF)



People are deciding the future of your wastewater system. Be a part of the conversation.

If you’re a customer of Sammamish Plateau Water, or a party wishing to develop within our service area, you should be aware of King County’s decision to reduce in priority the building of much-needed and long-planned improvements to the regional sewer system, and the impact that decision has on our ability to meet the needs of current and future customers.


The District contracts with the King County Wastewater Treatment Division to send our wastewater to their regional facilities for treatment and disposal.

Since the District began providing sewer service, King County has planned on the sewer flow from the Sammamish Plateau to be divided:

  • About half of the District’s wastewater would flow to the south around the south end of Lake Sammamish.
  • The other half would flow north through a future-planned northern connection known as the Sammamish Plateau Diversion.  See map 1

The District has designed its local sewer infrastructure anticipating a northern connection and for several decades has been giving King County notice that our facilities would be reaching capacity to continue to convey all sewerage to the one southerly regional connection.

The Issue. When do plans become a reality?


The District is outgrowing the capacity of the current sewer infrastructure. The District currently has only one connection point to the regional sewer conveyance system that is located in the southern portion of the District in the city of Issaquah. See map 2   

Since the District has only this one connection point available to the regional sewer conveyance system, we have to direct all wastewater flows from the entire service area to this one connection in the south end.

The District is relying on King County to expand its regional conveyance system to include additional sewer infrastructure to meet our growing needs and to serve our current and future customer base.

This is not a new issue.
  • For a number of years, the District has alerted the County that without the SPD, District facilities would soon reach capacity. We have now reached that point.

  • In 2013, the District advised County staff of the urgent need to construct this long-planned expansion known as the Sammamish Plateau Diversion (a.k.a. "North Diversion" or "Northern Diversion").

  • In 2016, the County advised the District that the Sammamish Plateau Diversion Project planning was underway, only to find out that in 2018, the County had removed the project from its Conveyance System Improvement Plan, citing funding limitations due to the operational failure of the County’s West Point Treatment Plant.

  • The decision to deprioritize the Sammamish Plateau Diversion was made without notice or conversations with the District.

The Challenge. Regional growth mandates require regional sewer infrastructure.


Because the District contracts with King County for sewage treatment and disposal services, we are required to align our long-term sewage system plans with those of the County so that we can send our wastewater flows to the regional sewer conveyance system. 

The District needs a second connection in the north to meet capacity needs and to serve its current and future customer base.

This second connection is a critical component of both the County’s and our long-term planning, and is key to following our District Wastewater Comprehensive Plan.

  • To meet the needs of our growing service area, and comply with the County’s Growth Management Act, the District is required to provide water and sewer service to those areas of growth.

  • This becomes more challenging without the additional capacity of a northern connection.

What’s at Stake? Sewer system capacity, resiliency, and the environment.


The District is in a position of having limited capacity to add new connections to the sewer system.

If we continue to add new connections to the sewer system, it could result in overflows affecting people's homes and/or the environment.

Knowing these risks, it would be irresponsible for us to continue to add new customers. Without these much-needed regional sewer system improvements, the District has placed a moratorium on additional customer growth in affected portions of the District with limited capacity. For more information on this sewer moratorium, click here.

Limited options during an emergency 

  • An important benefit from having a second connection in the north would be the ability to route wastewater to that connection if the pipeline in the south is compromised during an emergency incident.

  • Without having pipelines allowing for sewer flows to the north, the District is also placed in a position of increased risk for lengthy service disruptions from system failures, earthquakes, or other emergencies.

  • These are the tough realities we face if the County does not authorize, fund, and build the improvements needed to meet the District’s regional sewer conveyance needs.

King County’s offer will impact ratepayers.


On March 22, 2021, King County Councilmember Kathy Lambert, along with King County staff, attended a regular meeting of the District’s Board of Commissioners.

During this meeting: 

  • In spite of planning coordination for decades and the County’s recognition that our local capacity constraints have been impacted by a lack of regional capital improvements, the County finally made an offer to share 50% of the costs with the District to construct improvements to the District’s local sewer system. While the offer is generous, it results in shifting of costs from the regional system to our customers due to the County’s untimely programming of needed improvements.

  • County staff denied the District’s request to transfer District local assets to County ownership even though the District meets the County’s planning criteria. This denial perpetuates the District’s lack of equitable access to the regional conveyance system and continues to shift the cost burden to our customers for services that should be regionally provided and funded.

  • The County indicated that it will be reprogramming its work on the Sammamish Plateau Diversion Project with completion anticipated in 2030, but similar to past efforts and representations, the County cannot give assurance that the work will be funded or completed.

The Board of Commissioners is currently reviewing the County’s offer but has placed priority on identifying local solutions because we need assurances that our conveyance needs will be addressed, and the best way to ensure that is to take the lead in finding solutions.

Here are the latest updates.


June 9, 2021: The District is still waiting for a response from King County to a letter dated
April 30, 2021 in which the District accepted and requested clarification on the County’s cost-sharing proposal.  

June 7, 2021: District staff presented the Board of Commissioners with the Refined Scope of Work report for engineering services to address the sewer capacity issues in the North Sewer Service Area sewer system. The report includes information to support design of the interim improvements and management of the moratorium status. The District is also pursuing abatement (reduction) of Infiltration & Inflow (I&I) in the hopes of bringing additional capacity
to the system.  

May 24, 2021: The Board of Commissioners extended the sewer moratorium until August 23, 2021 to allow time to consider immediate, interim, and permanent improvements and their potential to provide additional capacity to the sewer system.  

March 29, 2021: The Board of Commissioners held a Special Meeting and Public Hearing to receive public comments from the residents, businesses, and cities impacted by the sewer capacity issues and sewer moratorium enacted by the District. During the Special Meeting, the Board approved an engineering contract to identify and consider immediate, interim, and permanent improvements.  

Follow these links to get additional facts.

View or download these supporting document files by clicking the corresponding links.


  • Overview Map: Affected sewer basins during 90-day moratorium.

  • Street-level Map: Affected sewer basins during 90-day moratorium.

  • Map 1: Location of proposed Sammamish Plateau Diversion (a.k.a. “North Diversion”)

  • Map 2: King County Regional Conveyance System

  • Map 3: Affected sewer service area 


  • 2021/Apr30  SPW to KC: From District’s Board President to Executive Constantine accepting the County’s proposal, subject to additional clarification and agreement on terms.

  • 2021/Mar22  KC to SPW: From the WTD Deputy Division Director to the District proposing a cost-sharing offer, committing to continue work on the Sammamish Plateau Diversion Project with completion anticipated in 2030, and denying the District’s request to transfer District local assets to County ownership.

  • 2021/Jan20  KC to SPW: Dow Constantine committing to resuming work on the Diversion Project in 2021 and 2022, to “propose full funding for the project in the 2022-2024 biennial budget process” and “potentially purchasing a large portion of the District’s local system.”

  • 2021/Jan05  SPW to KC: The District’s Board President expressing the District’s concern with “the County’s unilateral decision to deprioritize long-planned improvements to regional sewer conveyance infrastructure.”

  • 2019/Jul24   KC to SPW: The District’s and County’s signed agreement for North Diversion Interim Improvements Study “to identify necessary improvements in the local sewer system related to the deferral of the King County Wastewater Treatment Division’s Sammamish Plateau Diversion regional conveyance system improvement project.”

  • 2019/Apr16  SPW to KC: From the District’s Board President to the WTD’s Director including concerns that statements made in the County’s letter to the Mayor of Sammamish “discounts all of the Long-term collaborative planning efforts that have anticipated construction of a Northern Diversion and the financial investment the District has made anticipating a near term connection to the north.” 

  • 2019/Apr01  KC to COS: From King County’s WTD Director to the Mayor of Sammamish explaining the County’s decision to defer the Sammamish Plateau Diversion Project during the development of WTD’s 2019-2020 budget. 

  • 2018/Aug08  SPW to KC: From the District’s General Manager to the WTD’s Director responding to WTDs request for the District to participate with the County in conducting a consultant’s evaluation to update the District’s 2016 North Diversion Interim Improvement Evaluation Report. 

  • 2016/Sep26  SPW to KC: From District’s General Manager to the County sharing results of the Northern Diversion Interim Improvements Evaluation and expressing the need for the County to construct the Sammamish Plateau Diversion. 

  • 2014/May08  COS to KC: From the City of Sammamish’s City Manager to the WTD Director supporting the County’s plan for the Sammamish Plateau Diversion in order to “allow continued, uninterrupted development in our city, and avoid a potential moratorium” and “provide a vital benefit to our community.” 


  • PDF June 7, 2021: PowerPoint presentation - Refined Scope of Work Report

  • PDF June 7, 2021: Refined Scope of Work Report - North Sewer Service Area

  • PDF June 7, 2021: PowerPoint presentation - Infiltration and Inflow Abatement Options

  • PDF May 24, 2021: SPW Board Resolution #5030 - Sewer Moratorium Extension

  • PDF May 17, 2021: PowerPoint presentation - Sewer Moratorium Discussion

  • PDF Apr 19, 2021: SPW Board Resolution #5025 - Sewer Moratorium Amendment

  • PDF Mar 29, 2021: PowerPoint presentation from sewer moratorium Public Hearing

  • PDF Mar 12, 2021: Sewer Moratorium - Frequently Asked Questions (Updated 5/24/2021)

  • PDF Feb 22, 2021: Sammamish Plateau Water Board Resolution #5018 - Sewer Moratorium

  • PDF 2021 North Diversion Phase 1 Analysis 

  • PDF 2016 North Diversion Interim Improvement Evaluation 

  • PDF 2013 SPW Sewer Comprehensive Plan - Section 4.4 Future King County Facilities 

How to contact the District. 


For builders and property owners with questions about affected sewer basins and/or details of the moratorium, please email District staff at ConnectionInfo@spwater.org.

Media inquiries: Please call or email the District's Public Information Officer at 425-392-6256 PIO@spwater.org.

Board of Commissioners

The Sammamish Plateau Water Board of commissioners meets on the first, second, and third Mondays of the month at 3:30 p.m. For information on attending or providing comment for an upcoming Board meeting, click here.

Ryika Hooshangi, President
Lloyd Warren, Vice-President
Mary Shustov, Secretary
Tom Harman, Commissioner
Nav Otal, Commissioner

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