Caltrans implodes last of the old Bay Bridge piers in Saturday blast.

A 2017 photo shows demolition work done a year ago on one of the old Bay Bridge foundations. A 2017 photo shows demolition work done a year ago on one of the old Bay Bridge foundations. Photo: John Storey / Special To The Chronicle Photo: John Storey / Special To The Chronicle Image 1 of / 1 Caption Close Caltrans implodes last of the old Bay Bridge piers in Saturday blast. 1 / 1 Back to Gallery

The last remaining foundations of the eastern span of the old Bay Bridge were demolished Saturday, causing some traffic delays on the new bridge in the final chapter of the structure’s life before being transformed into boardwalks.

Rolling traffic closures lasted up to 30 minutes during the 11:20 a.m. implosions — which lasted less than 16 seconds — on both eastbound and westbound Interstate 80 at the Bay Bridge, according to the California Highway Patrol.

The Bay Bridge Bike Pedestrian Path reopened Saturday afternoon after the implosions occurred. The path was closed Wednesday for a final environmental review, Caltrans said.

As the two remaining piers were demolished, the explosions sent concrete and debris spinning to the bay floor. It was the next step toward building two boardwalks.

One marine foundation will be converted to a 140-foot long platform along Yerba Buena island, while three other demolished piers will be repurposed to create a 600-foot long boardwalk along the Oakland shoreline, Caltrans said.

“Once again, Caltrans has developed an innovative project that will convert a segment of existing infrastructure into a public asset,” said Caltrans director Laurie Berman. “The overlook and promenade will provide visitors with an up close appreciation of the bay.”

A bubble curtain over the water’s surface was installed before Saturday’s blast to minimize shock waves from the explosions. Next week, crews will use sonar technology to find and sweep up the debris from the bottom of the bay.

In all, the demolition of the old bridge and the construction of its replacement, which started in 2015, cost about $6 billion. Tearing down the last two piers will cost $52 million.

Sarah Ravani is a San Francisco Chronicle staff writer. Email: sravani@sfchronicle.com Twitter: @SarRavani