Basin 40 CIPP Sewer Lining Project Phase 1
Project Status
Click here to see status updates.
Background
Since the City’s sewer system was constructed in the 1950s and 1960s, many components are aging and require ongoing system improvements to ensure continued reliability and cost-effective operations. Throughout the years, NAASCO CCTV inspection data has been used to identify, prioritize, and develop a comprehensive rehabilitation and replacement program for the sewer conveyance system as it reaches the end of its useful life. These projects include manhole installation; pipe installation, rehabilitation, replacement, or lining; and smoke testing for inflow and infiltration (I/I).
Description
Inflow and infiltration is defined as excess groundwater and stormwater entering sewer pipes. This can either be from joint failure, cracks, holes, and faulty connections in the sewer pipes (groundwater infiltration) or it can come from roof downspouts, foundation drains, storm drain cross connections, and through manhole covers (stormwater inflow). Storm drainage systems and sewer systems are intended to be separate.
Sewer Basin 40 is one of the oldest areas of the City’s sanitary sewer system. It begins near the Mercer Island High School and Mary Waite Pool and flows east, down to Lake Washington. Most of Basin 40 is occupied by the large Mercerwood subdivision. City staff has identified Basin 40 as having excessive I/I during large rain events, which cause sewer system capacity issues. In the next couple of years, City staff will prioritize sewer system improvements in this area through pipe replacements and/or cured-in-place pipe (CIPP) rehabilitation. CIPP is a method of inserting a liner into existing sewer mains to extend the life of the main.
Project Timeline
Q3 of 2021 (design)
Q3-Q4 of 2022 (construction)
Estimated Budget
$1,000,000
Contact
George Fletcher, City of Mercer Island Project Manager: george.fletcher@mercerisland.gov
www.mercerisland.gov/sewer 22-33
Status Updates
April 14, 2023 Update
Next week, Insta-Pipe crews will be installing their final 20 sewer lateral service connection seals, called “top hats”, in the Mercerwood neighborhood, north of Mercerwood Drive. This will bring this sewer lining project very near to completion. Once this lateral work is completed, all the newly lined sewer mains will be video inspected for acceptance. All work should be finished by the end of April.
March 7, 2023 Update
Today, one lane of traffic will be closed on East Mercer Way near SE 40th Street to provide access to a sewer manhole. Flaggers will keep traffic moving in both directions by alternating traffic using one lane. Hours of work will be 8 AM to 5 PM.
January 31, 2023 Update
Construction is scheduled to begin tomorrow on the Basin 40 Sewer CIPP Lining Project Phase 1 within the Mercerwood neighborhood from 96th Ave SE east to N. Mercer Way, and SE 40th St. south to Mercerwood Dr. and go through April 2023. The contractor on this project is Insta-pipe and has worked within Mercer Island as recently as last summer. This project is a UV Cured-in-place sewer lining and rehab project which will include:
- Installing 4,310 LF of UV cured-in-place (CIPP) trenchless lining into the existing 8-inch diameter sewer main.
- Constructing 1 access pit over a sewer main to facilitate CIPP lining at address 4100 block of 96th Ave SE and installing 1 cleanout access point to the sewer, and backfill of the sewer access pit.
- Installing 59 service connection seals to seal the joint between the sewer main and the service.
Impacts to traffic will be intermittent flagger control and 1 lane closures.
August 2022 Update
Project is currently in the design phase. There are numerous sewer manholes and sewer mainline pipes within Sewer Basin 40 that are situated on private properties. City staff are in the process of contacting property owners to obtain Right of Entry agreements to their properties to access these sewer system features for the design/surveying and construction phases of the project.
May 2022 Update
At the kick-off meeting for design, Staheli presented their project approach and provided an updated schedule. The City anticipates receiving 50% design in the next couple of months.
April 2022 Update
In February, the consultant, Staheli Trenchless, delivered the final report with summaries of the condition of all sewer pipes. The City selected cured-in-place pipe (CIPP) as the rehabilitation method. It involves inserting a new liner inside the existing pipe. Staff and consultants will start the design phase this month.
February 2022 Update
Although Staheli Trenchless Consultants finished their review of sewer videos in October/November, there were still about 7,000 feet of sewer pipes that either had no video or it was too poor quality. The City decided to obtain the video for these segments using their CCTV camera truck. Videos have been collected, reviewed, and incorporated into the final report. Staff are currently reviewing the report and will initiate the second phase soon to add design services.
November 2021 Update
Photo: Fracture defect example
In October, Staheli Trenchless Consultants finished their review of over 12,500 linear feet of sewer videos. The primary defects are fractures, wall loss from corrosion and erosion, and offset joints/gaps. The City received the draft report summarizing the consultant’s findings and subsequent rehabilitation recommendations. Staff will review and anticipate receiving the final report in early December.
September 2021 Update
The City is currently negotiating a design contract with Staheli Trenchless Consultants. The project will be split in two phases, with the first phase reviewing historical data, including the City’s closed-circuit television (CCTV) videos to assess any defects in the pipes, and identifying the rehabilitation method. Later in the spring of 2022, the consultant will work on the second phase related to design.
Project Location (493 KB) 22-33 Project Awareness Signage (866 KB) Right of Entry Release form (76 KB) Right of Entry Form letter (248 KB)