Assessing the Effectiveness of a Bubble Curtain to Protect Aquatic Resources During Marine Blasting Demolition Work for the East Span of the San Francisco-Oakland Bay Bridge in San Francisco Bay, CA

Most estuaries and major rivers in California provide habitat for one or more fish species listed as threatened or endangered under the federal Endangered Species Act (ESA) or California ESA (CESA) and the potential for death or injury of fish resulting from underwater noise-generating construction activities has elevated public and resource agency concerns relative to effects on populations of these fish species. Most of the research and focus of impact analyses and protection efforts have been concentrated on pile driving activities. Marine foundation demolition using controlled blasting (implosion) and air bubble curtain attenuation on several piers of the former San Francisco-Oakland Bay Bridge was the first of its kind to be utilized in the San Francisco Bay and required the careful planning and consideration of potential impacts to the Bay's sensitive fish and aquatic resources.
In order to address these challenges, multiple caged fish studies were implemented to assess impacts from exposure of the Bay Bridge Pier E3, E4, and E5 implosions on fish resources, to test the effectiveness of a bubble curtain that surrounded the piers. A series of replicate cages, each containing about 40 hatchery-reared juvenile Chinook Salmon, were deployed at known distances between 120 and 3,300 feet from the piers and exposed to the implosions. Control cages were also deployed in the Bay but were removed prior to the implosion events. Cages were retrieved from the Bay and each was then assessed for mortality and injury based on observations of fish behavior and subsequent necropsies. Impairment or death did not vary with distance to the implosion. Necropsy confirmed that the test fish did not suffer blast-related barotrauma or damage. The type or magnitude of injuries found in the fish also did not depend on the distance from the blast. Caged fish had injuries consistent with handling stress and cage confinement.
The results of the study verified that underwater demolition using controlled blasting can be successfully used in San Francisco Bay (and potentially other water bodies) with the use of a properly functioning air bubble curtain attenuation. The bubble curtain was highly effective in avoiding blast-related injury or death of the test fish, and presumably of fish in the Bay at large.