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#PROJECTS: Big Creek Storage Tunnel (BCT)

Rock Excavation

The Big Creek Storage Tunnel (BCT) project is part of Project Clean Lake, our 25-year program to meet Clean Water Act standards and address water quality issues related to combined sewer overflow pollution. BCT is the seventh of seven new large-diameter tunnels that will control combined sewer overflows at 11 locations along Big Creek, Spring Creek, and Rocky River.

During construction, the project will have some short-term impacts on the community, including lane closures and traffic pattern changes (including bikeways), noise and vibration, dust, dirt, and/or mud, and disruption to community aesthetics. We will maintain updates here as provided by our project managers.

Project maps

See the image embedded above.


Design will begin in 2024. Construction will begin in Q3 of 2029 and the entire project will be completed in Q3 of 2034.


The construction contract estimate is $215 million.

Length and sizes

The Big Creek Storage Tunnel (BCT) will be 22,440 feet long and 20 feet in diameter.


The project will reduce CSO volumes discharged into the brook by over 280 million gallons annually and decrease flooding.

Community updates

To be provided.