Pump Station Rehabilitation & Replacement Project
Project Status
To help keep area residents informed of our construction progress, we will post project updates to this site on a regular basis. Click here to see status updates.
Project Details/Neighborhood
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Sewer Pump Stations (PS)s 19, 20, 21, 22, and 23 will be rehabilitated under this project.
- Due to the scale and complexity of the work, the City will take a phased approach, replacing one PS every two years.
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PS 20, located at 8790 85th Avenue SE at the southern tip of Mercer Island and along the Lake Washington shoreline, is in the poorest condition, so it will be the first to be rehabilitated.
Background
Mercer Island operates 18 sewer pump stations, which are located close to the shoreline (generally within 50 feet) and are used to convey flow through the City’s sewer lake line to King County’s South Pumping Station. The pump stations are constructed of concrete and are similar in design with most being a wet well/dry well configuration. There have not been substantial upgrades to the pump stations since their original construction in the 1960’s, except for pump station 4 (built in 2010), pump station 14 (rebuilt in 2014), and pump station 11 (currently being rebuilt by King County). Throughout the years the City has conducted regular maintenance of these pump stations, however rehabilitation or replacement (R&R) is imminent – some stations have capacity concerns while others have failing walls. In 2015, City staff conducted a pump station condition assessment, rating each station based on the consequence of failure. Most recently, in January of 2024, RH2 Engineering completed an assessment report which analyzed, ranked, and prioritized improvements for the five poorest condition stations. The assessment identified pump station 20 as being the most in need of rehabilitation.
Description
The work under this project includes various mechanical, structural, and electrical upgrades to rehabilitate the City’s sewer pump station 20. Replacement of existing pumps, fittings, piping, and valving, interior grating, vents, interior coatings, motor control panels, electrical service disconnect, distribution panels, circuit breakers, lighting transformers, and conductors serving the station are just a few of the improvements identified as necessary to extend the station’s service life another 50 years.
Project Timeline
PS 20: Planning/Design (May 2024 – January 2025)
Under Construction (February 2025 – July 2026)
Completed (July 2026)
PS 21: Tentative 2027-2028
PS 19: Tentative 2029-2030
PS 22: Tentative 2031-2032
PS 23: Tentative 2033-2034
Estimated Budget
$5,270,000 (PS 20)
Contact
Christopher Marks, City of Mercer Island Utilities Engineer: chris.marks@mercerisland.govs
Status Updates
October 2024
The vault inspection conducted on August 16 revealed significant defects in the station’s wet-well structure. This finding has considerable cost and construction implications, prompting the project team to re-evaluate design alternatives. Consequently, rather than rehabilitating the original 1966 wet-well dry-well station, the City will replace it with a modern submersible station, which is now the more cost-effective approach.
This new submersible station will provide several advantages, including:
- Lower construction costs
- Quieter operation
- Greater energy efficiency
- Reduced maintenance requirements
- Improved odor control
Additionally, the design will incorporate enhancements to the surrounding area, eliminate the need for a temporary sewer bypass during construction, and avoid the necessity for confined space entry by City operators. A preliminary site plan for the new station is available for viewing on the webpage. No impacts to the design schedule are anticipated as a result of this change.
August 21, 2024
Photo: RH2 Engineering design staff uses a pole-mounted inspection camera to assess the condition of the existing wet well structure.
On August 16th City Operations staff and RH2 Engineering conducted a thorough video inspection of the existing station Pump Station 20 wet well. The team also collected concrete samples for lab analysis and documented areas where extensive rehabilitation is needed. Repair and re-coating of the 58-year-old structure will occur simultaneously with rehabilitation of the rest of the station. RH2 will continue to work toward the 30 percent design milestone and pump selection for the rehabilitated station over the next couple months. PS 20 is located at the south end of the Island.
July 2024
Photos:
1: RH2 Engineering meets with City staff for a preliminary site investigation.
2: The wet-well access cover is removed. Evaluation of this confined space will occur during a future visit.
3: RH2 Engineering surveys the pump station dry-well.
Design for this project is underway. Upon contract execution, RH2 Engineering has reviewed relevant studies, as-builts, and other background information for the Pump Station 20 site. At the end of June, a site topographic survey was completed, and the following week, members from the design team surveyed the interior of the pump station. This preliminary work will be used to 3D model the existing vault and begin evaluating hydraulic data for the station. Work to reach 30 percent design and to identify candidate pumps will continue over the next couple of months.
May 28, 2024
Photo: Special design and construction considerations will be needed to rehabilitate PS 20’s concrete structure which directly abuts Lake Washington
In March of 2024, City staff solicited proposals from engineering design firms to rehabilitate pump station 20. The Request for Qualifications closed on 3/28/2024 after advertising for 3 weeks on the Builder’s Exchange of Washington and in the Seattle Daily Journal of Commerce. Only one proposal was received. After review and evaluation, the sole proposer, RH2 Engineering, Inc., was identified as the most qualified firm. The City intends to enter into a contract with RH2 Engineering at this time. Design work for this project is expected to begin at the beginning of June and take approximately 9 months to complete.
SU0128 project location (2 MB) PS 20 Preliminary Site Plan (354 KB)