A Caltrans plan to demolish the largest pier of the old eastern span of the Bay Bridge using explosives could spread concrete debris through the Bay, a staff scientist with an environmental watchdog group said Wednesday.
Ian Wren, a staff scientist with Baykeeper, will raise the concerns during a Thursday meeting of the San Francisco Bay Conservation and Development Commission in San Francisco.
"This cost-saving operation is without precedent in San Francisco Bay, and it seems the Bay will end up paying the price to recoup money spent on cost over-runs and mistakes in the new bridge construction process," Wren said in a statement today.
The plan involves demolishing Pier E3, a 268-foot chunk of concrete set deeply in the Bay mud, using 600 small explosives, which would pulverize the concrete above the seabed.
An "air curtain" of pipes blowing compressed air set around the pier would contain the debris and direct it into the pier's hollow chambers below the surface, according to Caltrans. The pier is set 165 feet below the mudline.
The debris would then be entombed in the bottom of the Bay.
But Wren has said he is skeptical whether the air curtain will actually be able to contain the debris and fears the surrounding water will be contaminated with concrete dust and rubble.
Another concern is how the blast could affect surrounding wildlife -- particularly seals, sea lions and porpoises -- that could be harmed by the sound of the blast.
To address that, Caltrans chose November for the implosion, the time when there are fewest of those animals in the Bay. In addition, a radius of more than one mile will need to be monitored to make sure there are no animals nearby. If animals are spotted, the implosion will be postponed.
Wren has said that he is mostly satisfied with the efforts to mitigate the effects on wildlife, but remains skeptical that this is the most environmentally sound way of demolishing the pier. If the air bubble does not in fact contain the blast, his group will advocate against using this method for demolishing the remaining 21 smaller piers.
"The most environmentally sound method for taking down the old Bay Bridge piers is mechanical removal, as originally proposed and as the original permits approved," Wren said. "If the first implosion harms the Bay, Baykeeper will work to ensure that a more environmentally sound method is used to dismantle the remaining piers."
The hearing on the permit for the implosion plan is scheduled for 1 p.m. Thursday at the San Francisco Ferry Building.