City of Mercer Island, Washington - Home City of Mercer Island, Washington - Home Facebook Twitter YouTube
site map
Back to City and Regional Projects

Operating & Capital Financial Challenges
Light Rail (East Link)
I-90 Issues
Sound Transit Park-and-Ride
Residential Development Standards Update
Mercer Island Center for the Arts (MICA)
Capital Improvement Program
Street, Pedestrian & Bicycle Facilities
Transportation Improvement Program (TIP)
Transportation Benefit District
Renton Municipal Airport

Calendar Events
RFPs & Bids

9611 SE 36th Street
Mercer Island, WA 98040
Phone: 206.275.7600
Fax: 206.276.7663
Notify me by Email
Sewer Lake Line Replacement Project

Sewer Lakeline Replacement Project
Sewer Lakeline Replacement Project

Lake Line Replacement Project


[ Work on the City of Mercer Island’s Sewer Lake Line Replacement Project, the largest capital project in the City’s history, wrapped up late in 2010.]


This project will replace approximately 7,000 linear feet of sewer line located in Lake Washington along the northwest shoreline of the Island (known as Reach 3, extending from SE 32nd Street to Roanoke Way). The existing sewer line was installed in the mid-1950s, and is constructed of asbestos-cement (AC) material. It has been experiencing ongoing pipeline deterioration, capacity deficiencies and operation and maintenance problems.


The three main components of the project construction include replacement of the lake line sewer main and side sewers, relocation of Pump Station No. 4, and environmental mitigation.


Manson Construction and their subcontractors Frank Coluccio Company and Global Diving will continue to work to install side sewer connections to homes beginning July 2, 2010. 


Safety is critically important. To protect divers, please keep boats at least 500 feet from all work areas. Also take the opportunity to become familiar with the buoys we will use later this summer to mark areas you should avoid.


Project Overview and Photos

This presentation provides a good overview of the project along with numerous photos. It identifies the project elements and notes some of the many challenges contractors face. It also provides information about the new Pump Station. 


We Need to Hear From You

If you have an invisible dog fence, please let City officials know its location by calling (206) 275-7813. We don’t want to disturb your fence during construction, but we cannot accomplish this if we don’t know where it is. In addition, let us know if there is anything else underwater beyond the end of your dock that might tangle dredging equipment, such as boat anchors, irrigation lines or any other lines.


Construction Equipment

Construction requires mobilization of several pieces of large equipment, including dredges, derrick barges, floats and tugs. This presentation shows you the equipment that is being used for the lake line construction.

Park Closures

Manson Construction is using SE 32nd/Proctor Landing for construction staging. Therefore, the Proctor Landing park site will be closed to public use for the duration of the project. The area under I-90 is also closed through 2010.


There are several other parks and street ends which residents may use along 60th Avenue SE, including:

  • Garfield Landing – SE 30th and 60th Avenue SE
  • Slater Park – SE 29th and 60th Avenue SE
  • Calkins Landing – SE 28th and 60th Avenue SE

All three areas are open and available for people to use during the summer. The City regrets any inconvenience for closures at Proctor Landing and I-90, but we need to provide a safe and secure site for construction activities.


Project Updates

Learn more and follow our progress with the lake line construction.

June 2010

April 2010

January 2010

August 2009

June 2009

May 2009

March 2009




Understanding Mercer Island's Sanitary Sewer System

Mercer Island's sewer system has two main pieces:

  1. Upland areas of the Island are served by a conventional gravity collection system. This system collects flws from sewer customers and then routes the sewage to a lakeline system that circles the Island. Most of the upland collection system was constructed in the mid-1960s.


  2. The lakeline sewer system is generally located five to ten feet offshore, and serves as both a collection system (collecting sewage from homes along the shoreline) as well as a conveyance system, routing sewage collected from the upland areas around the Island. The lakeline system uses pumps to convey the sewage around the Island, and to flush the system piping. Flows are pumped to the Metro Wastewater Treatment facility in Renton from two locations on the Island.
Sewer pipes located in Reaches 3 and 4 of the lakeline system are some of the oldest in the system, having been installed between 1956 and 1961. The original lakeline pipes were made of asbestos concrete (AC). The system included about three miles of piping and four pump stations.

In 1970, about 3,000 feet of lakeline AC piping was replaced with cast iron (CI) piping in the Lake between Roanoke Way and the King County Inlet Facility.


Design Alternatives Considered

In 2002, the City of Mercer Island hired Economic and Engineering Services, Inc. (EES) to study the feasibility of the project. A final report was published in September 2002.

The Feasibility Study identified a number of lakeline replacement construction alternatives. These alternatives differ greatly, depending on:

  • Location of the new sewer line
  • Whether the new system has one or two pipes
  • Construction method used for building the new system
    Options Considered All options have been studied in detail.  In 2003, the City hired TetraTech/KCM, Inc. to complete the environmental and permitting phases of the project.  With the assistance of Jones and Stokes, the Final Environmental Statement (FEIS), which was issued in March 2005, further evaluated the three options listed.  The In-Lake (dual pipeline) alternative is identified as the City's preferred alternative in the FEIS.



City of Mercer Island Washington | All Rights Reserved © 2019| Privacy Policy | printer friendly version Printer friendly version | Site Handcrafted in Ashland, Oregon by Project A