Sammamish Plateau Water has temporarily paused new sewer
connections for 90 days 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 90-day moratorium, click here.

Sewer Moratorium - Frequently Asked Questions (PDF)

Public Hearing:

Monday, March 29, 2021 at 6:00pm - For details, click here.



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 may have to place a moratorium on additional customer growth in affected portions of the District with limited capacity. See map 3

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.

Follow these links to get the 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/Jan20  KC to SPW: Sammamish Plateau Northern Diversion Project

  • 2021/Jan05  SPW to KC: Regional Conveyance Infrastructure - Sammamish Plateau Diversion

  • 2019/Jul24   KC to SPW: Agreement for North Diversion Interim Improvements Study

  • 2019/Apr16  SPW to KC: Northern Diversion Project re: 4/1/19 Letter to City of Sammamish 

  • 2019/Apr01  KC to COS: KCWTD Capital Improvements – Sammamish Plateau Diversion 

  • 2018/Apr08  SPW to KC: Northern Diversion Interim Improvements 

  • 2016/Sep26  SPW to KC: Sammamish Plateau Diversion 

  • 2014/May08  COS to KC: Sammamish Plateau Water and Sewer District – Northern Diversion 


  • PDF Mar 12, 2021: Sewer Moratorium - Frequently Asked Questions

  • 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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