Caltrans aims for early Saturday on old Bay Bridge pier blast

Preparations for an implosion continues on the E-3 pier of the old Bay Bridge in San Francisco, Calif. on Wednesday, Nov. 11, 2015. A demoliton team will detonate a number of charges below the surface of the bay to demolish the old piling on Saturday morning. less Preparations for an implosion continues on the E-3 pier of the old Bay Bridge in San Francisco, Calif. on Wednesday, Nov. 11, 2015. A demoliton team will detonate a number of charges below the surface of the ... more Photo: Paul Chinn, The Chronicle Buy photo Photo: Paul Chinn, The Chronicle Image 1 of / 22 Caption Close Caltrans aims for early Saturday on old Bay Bridge pier blast 1 / 22 Back to Gallery

The once-delayed demolition of the largest remaining pier of the old Bay Bridge eastern span is now set for early Saturday, as officials look to avoid a monster traffic jam when the new bridge is shut down for up to a half hour, Caltrans said Thursday.

The six-second implosion is scheduled to happen between 6:45 and 7 a.m. to take advantage of slack tide, limited wildlife activity and light traffic. Officials at first were looking at a 1 p.m. demolition but worried that it could take a greater toll on wildlife and blanched at the idea of closing the Bay Bridge in both directions in the middle of the day — although there’s still a small chance the blast will happen then.

“We are working very closely with the (California Highway Patrol) to make sure there is as little inconvenience as possible to the traveling public,” said Leah Robinson-Leach, Caltrans’ spokeswoman for the bridge project.

Caltrans says it is confident that a wooden and steel mat placed atop the 80-by-140-foot concrete pier will keep debris from flying onto the new span when nearly 600 charges of dyna mite — totaling 20,000 pounds — are detonated. But officials are taking no chances.

In addition to stopping Bay Bridge traffic 15 minutes before the implosion window opens, the CHP will close the bicycle and pedestrian path on the south side of the eastern span Friday night. BART will halt service through the Transbay Tube for a short time when the blast happens, and boats will be kept at least 1,500 feet away.

Entombing debris

The plan is to knock down the top 50 feet of the pier and entomb the debris at the base of the 225-foot-deep remainder of the pier. Other debris will be contained by a boom around the pier.

A flotilla of wildlife observers will be monitoring the area for last-minute interlopers, including diving birds and marine mammals, and officials may halt the implosion on short notice if one appears.

Scientists will be on the lookout in particular for two diving birds, the endangered least tern and the protected brown pelican. If either is diving within 500 feet of the pier, the implosion could be put off while monitors use laser pointers and air horns to try to shoo it away. Caltrans hopes harbor seals and sea lions will be deterred by a ring of noise-emitting buoys.

Engineers will await the target animal’s exit from the area, and Caltrans will try again. One possibility, they caution, is that the implosion will be put off until the next slack tide in the dreaded 1 p.m. window. The blast could also be postponed to Sunday.

Doomed fish

Caltrans hopes to blunt the underwater explosion by generating a curtain of air bubbles, but it still expects the pressure wave to kill as many as 1,775 endangered longfin smelt, and possibly other species. The implosion will generate a short-lived plume of fine concrete dust in the bay, but that will quickly dissipate, officials say.

Caltrans opted to go the implosion route rather than demolishing the pier by machine, which would take as long as four years and probably kill more wildlife than the blast would, the agency said. If Saturday’s blast is a success, Caltrans expects to do the same to as many as 12 remaining piers from the old eastern span.

November is an ideal time to attempt the big pier demolition, Caltrans said, because many seasonal birds have left for the winter. The birds that are in the area are less active early in the day than at 1 p.m., Robinson-Leach said.

Ideal time

She said Caltrans chose the early-morning time to limit damage to “every aspect of the environment.”

“This is not only the time of the month to do it, but the time of the day to do it,” she said. “We look forward to this highly orchestrated operation being successful.”

Caltrans had scheduled the implosion for last Saturday, but the packages containing dynamite that will be lowered into cavities in the old pier were deemed to be too flimsy and prone to falling apart before the blast. A new batch was ordered, and Caltrans says these packages are in place and should be fine.

There will probably be little to see from above when the implosion happens, Caltrans said. The agency is setting up an underwater camera from a nearby pier that may capture the blast.

“We are encouraging the public to watch it online,” Robinson-Leach said. The easiest way will be to search YouTube for E3 Implosion.

Jaxon Van Derbeken is a San Francisco Chronicle staff writer. E-mail: jvanderbeken@sfchronicle.com

Imploding a pier

When: Scheduled for Saturday, between 6:45 and 7 a.m.

Bridge: The California Highway Patrol will block traffic 15 minutes before the scheduled implosion. The bicycle and pedestrian path will be closed beginning Friday night.

BART: Transbay Tube will be shut down briefly before the blast.

Maritime: Ships and boats will be kept 1,500 feet from the pier.