During development of our 10-year Capital Plan, a condition assessment of the existing force main was conducted and based on those results decided to focus our efforts on a new Channel Force Main Redundancy Project in place of the Central Bayside System Improvement Project. The Channel Force Main Redundancy Project will address risks associated with the aging force main and provide redundancy for this critical sewer system component.
We are in the early planning stages of evaluating alternatives. In addition, a smaller Channel Force Main Intertie Improvement Project has also been initiated to provide redundancy in the downstream (most vulnerable) third of the force main in a shorter timeframe.
CBSIP at a Glance
The Project Seeks to:
• Improve overall system reliability by improving resilience to seismic events
• Improve water quality along the shores of the Bay by reducing combined sewer discharges
• Increase operational flexibility to help meet goals related to adaptation to climate change and sea level rise
Channel Tunnel - Convey flows from a shaft near the Channel Pump Station to the Central Bayside Pump Station
Central Bayside Pump Station - Pump flows from the Channel Tunnel to the Southeast Treatment Plant
Three Connection Components
• Northern Connection tunnel to convey flows from the Channel Pump Station to a shaft at the northern end of the Channel Tunnel
•Two Southern Connection force mains to convey flows from the Central Bayside Pump Station to the Southeast Treatment Plant
• Intertie Connection at the Channel Tunnel to convey wet weather flows from the Islais Creek Transport/Storage Box to the Channel Tunnel
Channel Pump Station
The Central Bayside System Improvement Project (CBSIP) is a part of the Sewer System Improvement Program (SSIP), and is a critical element of the City’s efforts to upgrade the aging and seismically vulnerable combined sewer system on the Bayside.
As part of the Bayside Collections System, the Channel Force Main transports 64% of wastewater from homes and businesses on the Bayside to the Southeast Treatment Plant. This important piece of infrastructure is a weak link on the Bayside as it is vulnerable to seismic damage, and has suffered several failures since the 1989 Loma Prieta earthquake.
To address this need, the design team is investigating a potential tunnel to provide reliable gravity conveyance and storage of wastewater flows from the Channel Pump Station (located near AT&T Park) to the Southeast Treatment Plant. Channel Pump Station improvements and a new pump station near Islais Creek are also under consideration.
|Benefits of a Tunnel
- Less disruption to vehicle and pedestrian traffic.
- Less noise along the alignment of the tunnel. Construction noise is reduced because it’s deep underground.
- Less construction vibration. The excavation work is far underground and expected to be undetectable at the ground surface. It will be considerably less disruptive than work in a trench at street level.
- Less seismic risk. During seismic activities soft soils move more than harder, soils or rock. These movements have the potential to damage or break infrastructure. At the depth of the tunnel the ground conditions are harder and the majority of the tunnel is in rock. This reduces the likelihood and/or magnitude of damage to the tunnel compared to a shallow pipe.
The project team is currently working towards finalizing 35% Design in early 2018. Funding for construction of this project is not yet approved. The decision to authorize continued work toward 65% Design will be made in late 2020. Please continue to visit the project website for schedule updates.
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