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Ship Canal Water Quality CSO Tunnel 

Seattle Public Utilities

Seattle, Washington
Estimated Cost:
$158 million
Value Analysis
Market Sector:
Facility Specialty:
Tunnels and Utilities


The purpose of the Ship Canal Water Quality Project is to provide offline storage of Combined Sewer Outflow for five Seattle Public Utilities and two King County Department of Natural Resources and Parks basins. The purpose of the project was to meet regulatory control standards, to limit untreated discharge.

The total control volume to be achieved is 15.24 million gallons (MG). The facility now meets water quality standard and is to be verified by post construction monitoring. 

Offline storage will be provided with a deep storage tunnel constructed between the Ballard and Wallingford CSO areas on the north side of the Ship Canal.

The main components of the Ship Canal Water Quality Project include the storage tunnel and appurtenances, conveyance facilities to convey flows into the tunnel, and a tunnel pumping effluent line to drain flows away from the tunnel.

MENG Analysis developed $31,846,000 worth of cost saving proposals.

Key Proposals:

  • Revisions to reduce pump requirements

  • Alternative considerations to improve maintenance

  • Options to reduce size, increase functionality, simplify and improve design

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