Sewer Pump Station 19 & 21 Replacement Project

Project Details/Neighborhood 

Sewer Pump Stations (PS) 19 and 21 will be replaced under this project. Both stations are located on the Lake Washington shoreline at the southern portion of the Island. PS 19 is located at 7697 W Mercer Way and PS 21 is located at 8000 Avalon Dr.

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), pump station 11 (rebuilt in 2026), and pump station 20 (scheduled for rebuild in 2027)

The City has performed regular maintenance on its sewer pump stations for many years; however, several stations now require rehabilitation or replacement due to capacity limitations and deteriorating structural walls. In 2015, City staff completed a condition assessment that evaluated each station based on the consequence of failure. A follow-up assessment completed in January 2024 analyzed and prioritized improvements for the five stations in the poorest condition, identifying Pump Stations 19 and 21 as the next candidates for replacement.

Description

This project includes the rehabilitation and replacement of Sewer Pump Stations 19 and 21. Both wet-well/dry-well stations were originally constructed in 1966 and have reached the end of their useful service life. The project will include replacing pumps, piping, mechanical systems, and associated electrical and control equipment; repairing, rehabilitating, or replacing the existing concrete vault structures; and completing utility reconfiguration, system modernization, and site improvements. The goal of the project is to extend the service life of each station by approximately 50 years while minimizing impacts to nearby residents and the shoreline environment.

Project Timeline
Planning/Permitting/Design (March 2026 – December 2027)

Construction (January 2028 – December 2029)

Estimated Budget

$12,260,000

Contact:

Christopher Marks, City of Mercer Island Utilities Engineer: chris.marks@mercerisland.gov