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Overview: The Bridge and the Environment
Long before the first worker showed up for day one on the new East Span job, more than 30 studies had been completed to assess impacts related to air quality, noise, vibration, traffic circulation, land use, biological resources endangered species, hazardous waste and historical and cultural resources.
With the help of those studies, Caltrans and several agencies coordinated and approved a series of measures to reduce the impact of construction, and of the very presence of the bridge itself, on the Bay environment.
For example, trusses beneath the existing bridge already host the second largest double-crested Cormorant colony in Northern California. The new East Span will have its own man-made nesting habitat for Cormorants tucked away from public view under the span.
More directly impacted by construction will be marine life. Underwater sound waves caused by pile driving can stress and kill fish. To reduce that threat, Caltrans requires pile driving contractors to use techniques that lessen the danger.
One such technique is to use a dewatered cofferdam. A cofferdam is a solid vertical barrier that prevents water from entering the work area. The barrier is installed, water is pumped out and the result is essentially a hole in the water that provides a dry workplace and reduces the sound impacts of the pile driving.
Another technique is to install a bubble curtain system. During pile driving, an air compressor pumps water into three perforated pipelines that surround each pile. This creates a continuous stream of bubbles that decreases the pressure of sound waves on nearby fish.
Caltrans is also taking special precautions to protect fish and habitat during dredging required for barge access and pier construction and during the dismantling of the old bridge. Because dredging can make the water murky enough to harm fish, Caltrans routinely checks the turbidity of the dredging area and, when feasible, is limiting dredging to specific time periods. Caltrans has a website that provides timely information about their biological mitigation and monitoring efforts. Visit the Caltrans Biological Mitigation website.
Caltrans is also restoring eelgrass beds at the Oakland landing area. Eelgrass beds help stabilize shorelines from tidal action and provide fish habitat. Caltrans used the experimental technique of transplanting the beds from the construction site to nearby locations where they will be undisturbed by construction.
Caltrans will also be preserving the history of the existing bridge and protecting historical and archeological sites on Yerba Buena Island. No historic buildings will be moved or demolished, particularly the former residence of Admiral Chester A. Nimitz. The house sits under the planned transition structure that will link the Suspension section with the Yerba Buena Tunnel.
In addition, Caltrans is working with the Oakland Museum to create exhibits about the old East Span.