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The Cityis installing a new water supply pipeline to improve theoverall resiliency of the City’s water system.The new water supply line will replace a section of the aging Seattle Public Utilitiestransmission linethat currently serves Mercer Island by deliveringwater to the City’s reservoirs. The new water supply line will be fully owned and operated by the City. See the Project Map here.
In addition to the new water supply line, this project includesimprovements to other City infrastructure in the same corridor including replacement of an asbestos-cement (AC) watermain, roadway paving and sidewalk enhancements. Combining these improvements into one project improvesproject efficiency, scheduling, reduces costs and overall construction impacts.
Follow this page for details of the design and construction of the new water supplypipeline, as well as neighborhood and traffic impacts through the project.
The Cityis installing a new water supply pipeline to improve theoverall resiliency of the City’s water system.The new water supply line will replace a section of the aging Seattle Public Utilitiestransmission linethat currently serves Mercer Island by deliveringwater to the City’s reservoirs. The new water supply line will be fully owned and operated by the City. See the Project Map here.
In addition to the new water supply line, this project includesimprovements to other City infrastructure in the same corridor including replacement of an asbestos-cement (AC) watermain, roadway paving and sidewalk enhancements. Combining these improvements into one project improvesproject efficiency, scheduling, reduces costs and overall construction impacts.
Follow this page for details of the design and construction of the new water supplypipeline, as well as neighborhood and traffic impacts through the project.
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At the October 1, 2024 City Council Meeting, City staff presented recommended actions to improve resiliency of the permanent water transmission line from Seattle Public Utilities (see AB 6530). The 24-inch concrete cylinder water transmission line located in the SE 40th Street right-of-way was constructed in 1956 and has required several leak repairs over the years. The City and Shorewood Apartments are the two wholesale customers served by SPU’s water transmission line. Given the overwhelming cost responsibility held by the City, and the importance of this water transmission line, the City began exploring options to replace this segment of pipe with a stronger, earthquake resistant transmission line in an alternative alignment.
This City considered several options, details of which can be viewed here.After careful consideration, the City Council approved the design and construction of a new 24-inch earth-quake resistant supply line to replace the existing SPU supply line.The location of the new 24-inch supply line corresponds with several previously planned projects. To reduce construction costs, schedule, and impacts, this project was combined with these previously planned projects.
City Council voted to direct staff to include the design and construction of a new 24-inch transmission line in the 2025- 2030 Capital Improvement Plan. City staff will negotiate a preferred pipeline alignment and ownership from Seattle Public Utilities and identify long-term solutions to serve the Shorewood Apartments.
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In the spring of 2024, a leak from the Seattle Public Utilities (SPU) 24-inch diameter water supply line on Mercer Island was discovered. The City Manager declared a Local Emergency due to the reduction in the supply of incoming potable water to Mercer Island, and immediate steps were taken to mitigate the impacts of the leak, ensure safety of the site, and repairs were made to the line over the summer of 2024.
Given the overwhelming cost responsibility held by the City, and the importance of this water supply line, the City began exploring options to replace this segment of the SPU line with a stronger, earthquake resistant supply line in an alternative alignment.
Additional information on the leak and other past issues with the SPU line can be viewed here.
