Environmental Science Associates (ESA), a leading environmental consulting firm, participated in Saturday’s carefully executed implosion of Pier E3, the largest of the piers on the San Francisco-Oakland Bay Bridge’s Old East Span. Pier E3 contains the largest caisson used to support the cantilevered section of the Old East Span, and is one of about 20 piers that will need to be removed as part of the demolition process.
According to Caltrans, “in the early morning at slack tide, years of preparation, more than half-a-dozen permits, and thousands of hours of labor culminated in what appears to be a successful implosion. In just six seconds, nearly 600 controlled charges weakened the 50-feet of Pier E3 which stood above the bay floor, allowing gravity to collapse the tower into its hollow casing below the mudline.”
The controlled underwater implosion was intended to demolish the E3 caisson in place, but in a manner that would result in disposal of nearly all the waste concrete within the walls of caisson buried in the mud beneath the Bay bottom and with as minimal as possible impact to surrounding marine life. While the implosion itself lasted just six seconds, the carefully orchestrated demolition required countless hours of preparation and set-up, including surrounding the caisson with an extensive bubble curtain, which was estimated to reduce the intensity of the pressure waves generated by the charges by about 80%. Boreholes were drilled into the foundation to insert over 600 hundred charges into the concrete foundation.
ESA biologists conducted sonar monitoring of the surrounding area to characterize the local fisheries. In addition, ESA’s fish biologists coordinated an extensive trawling assessment following the demolition event that was conducted by three Moss Landing Marine Lab vessels. ESA designed and executed a Caged Fish Study at the site that measured injury and survival rates from exposure to the blast at known distances from the pier. This study was closely coordinated with near- and far-field hydroacoustic monitoring studies and the combined results will be used to inform the client and project team on the potential effects to adjacent aquatic resources by the implosion.
“This is a pioneering example of creative environmental problem-solving,” said Gary Oates, ESA’s President. “Assisting our clients in finding and implementing new environmental solutions to address old problems is something we’re proud to be a part of and strive to achieve. This is one high-profile example of what ESA practices every day as we work to meet the rising environmental challenges facing our clients.”