What is a Wastewater Comprehensive Plan?
A wastewater comprehensive plan considers both the short and long term needs for providing sanitary sewer service to a specific area. In this case, the area is the urban area of the District. The plan is intended to guide the District in decisions made regarding the expansion of sanitary sewer service, and also set the standards under which this expansion will take place.
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How will the Wastewater Comprehensive Plan be used by the District?
The Plan sets policies that direct District staff in decisions that are made regarding the extension of sewer service. The policies cover:

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What is the District's policy for providing sewers to our area?
The District generally provides sewer based on requests from property owners interested in obtaining sewer service. Sewer extensions are most frequently done as Developer Extension Agreements, where an individual may extend the sewer to reach their property, or as a Utility Local Improvement District, where a neighborhood petitions the District to install sewers.
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How is sewering of unsewered areas prioritized?
There is no District priority set at this time. Project timing is set by neighborhood or developer requests, or by the timing of a road project that includes sewer construction.
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How can I give my opinion on sewer service expansion?
You may write or e-mail the District at:
Sammamish Plateau Water & Sewer District
1510 - 228th Avenue SE
Sammamish, WA 98075

Commissioners@sammplat.wa.org

You may also speak to the Board of Commissioners in person at one of their regular meetings. The Board meets the first three Mondays of each month at 3 PM.
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Where can I get information on upcoming sewer projects?
The District has a map showing current projects on the District web site. There is an accompanying project description also on the web site. (www.sammplat.wa.org, then Projects) These projects are in various stages of development, from planning to design to construction.

The District may also put in sewers as part of a Capital Improvement program. The most frequent example of these situations are when sewers are installed as part of a road improvement program. The installation of sewers with the recent 228th Avenue widening is an example.
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Are existing sewer customers paying for sewers that serve new growth?
When a customer is connected to the District's sewer system they pay certain connection fees. One of the connection charges, the General Facility Charge, pays for the larger facilities that serve large segments of the community. These facilities are sized for growth.

The sewer rates, however, are based on the ability to operate and maintain the sewer system providing service to existing customers.
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Will this plan lead to more growth?
The Plan does not lead to more growth, but is developed in response to decisions made by agencies that can make decisions about land use. The District gets direction on how growth within the urban area may occur from the King County, City of Sammamish and City of Issaquah's Comprehensive Plans.

The City of Sammamish's initial Comprehensive Plan is being developed at this time. The previously adopted King County Comprehensive Plan will be used until the City of Sammamish Plan is completed.
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Where is the "Urban Area" of the District and how did it get to be Urban?
The Urban Area was designated by King County as part of the 1994 King County Comprehensive Plan. King County designated the Urban Area, at least in part in response to the State's Growth Management Act (GMA).

The other designation within the District's service area is rural. Sanitary sewer service is not allowed in the rural area, except in cases where the County has considered a specific request and allowed the service to be extended.
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What are Sanitary Sewers?
Sanitary sewers are a series of pipes, manholes, lift stations and other facilities that carry sewage from residences, businesses, and public institutions to a treatment plant where the sewage can be cleaned before it is discharged back into the environment.

Sanitary sewers are not installed to carry storm drainage, the runoff that occurs after rain or snow. In fact they are designed specifically to keep storm drainage out of the system.

There are some older communities where a sewer system collects both storm drainage and sewage. These are called combined sewer systems. Combined sewer systems are generally not allowed in the District's service area.
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What is the Difference Between Sewer & Septic Systems?
A sanitary sewer system collects sewage from a large area and carries the waste to a central location for treatment and discharge. Sanitary sewer systems can be as small as a single subdivision or regional systems that treat wastewater from many square miles of area.

Septic systems are on-site systems that dispose of household wastewater into the ground, usually through a system located on the same property where it is generated. Normally a septic system will start with a septic (or holding) tank where natural bacterial action starts to decompose the sewage. Undigested solids may float or fall to the bottom of the tank. The effluent from the middle layer of the septic tank is piped to the drainfield portion of the septic system. The drainfield is a series of perforated pipes in the ground. The effluent flows out of the pipes into the soil, where it is further treated as it filters through the ground.
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What is the conceptual sewer layout?
The conceptual sewer layout represents where sewers could be installed when the decision is made to extend sewer service. Aerial Backography and photography combined with a general knowledge of the area has been used to develop the layout. Detailed design has not been done during development of the conceptual layout.
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What is a sewer basin?
A sewer basin is an area from which all of the sewage is collected to a single point. Sewer basins may generally follow surface water drainage basins, but can diverge when a sewer pipe takes the sewage over a drainage basin boundary.

The District has designated 13 sewer basins within its service area for purposes of this plan.
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Why are sewers installed?
Sanitary sewers are installed to provide wastewater disposal. The other method of wastewater disposal commonly used in this area is on-site septic systems.

King County's 1994 Comprehensive Plan dictated that all urban areas should be provided wastewater service with sanitary sewers. Therefore, sanitary sewers are required to be installed for new construction within the urban area.

However, there are portions of the urban area in the District where the sewer systems have not been installed yet and are still quite far away. In these situations, septic systems may be allowed as a temporary situation, until sanitary sewers are installed.
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How does the District decide when to install sewers?
Sewers are generally installed in response to requests for sewer service. These requests may be associated with a new development or to add sanitary sewer to existing neighborhoods that are partially or fully developed already. The District may also install sewers in conjunction with road projects or to augment existing sewer systems that are in need of repair or increased capacity.
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How does the District decide where to install sewers?
The District has divided the urban area of the District into several sewer basins. When the District is deciding where sewers should be installed within the sewer basin several factors are considered together.

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How does the District design new sewer systems?
When an extension to the sewer system is required the District consults the conceptual sewer layout to determine the likely location of new sewers.
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Will Wastewater facilities impact wetlands, streams, or other sensitive areas?
Sanitary sewer systems usually work with gravity flow. Because the sewer system must go downhill so gravity can work they frequently come in close proximity to other gravity driven systems, like streams. The sewer design attempts to avoid as many sensitive areas as possible, but to maintain gravity flow sensitive areas must be crossed occasionally.
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Does the District treat the sewage it collects?
No, the District just collects the sewage and then discharges it to the King County system. The current discharge point is located on SE 56th Street at the entrance to Lake Sammamish State Park.
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Where is the sewage treated and disposed?
The sewage collected from the District is transferred through the King County system to the Renton Treatment Plant. After being treated at the Renton Treatment Plant the effluent is disposed of in Puget Sound. Some of the Renton effluent is treated to an advanced level and reclaimed for industrial cooling and landscape-related uses.
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