Largest remaining pier in eastern span of old bay bridge demolished

SAN FRANCISCO (KGO) -- Caltrans has completed the implosion of a pier of the old eastern span of the Bay Bridge at 7:17 a.m. Saturday.

The implosion was a highly-choreographed but short six-second sequence that was overseen by a cast of hundreds.

WATCH: Old Bay Bridge demolition options

It took 20,000 pounds of dynamite, strategically placed, to imploded the underwater support pier, which was five-stories tall and part of the old Bay Bridge.

"We had a significant monitoring system in place that allowed us to do the implosion," said Leah Robinson-Leach, a Bay Bridge spokesperson.

The California Department of Transportation set a wooden and steel mat on top of the 80-by-140-foot concrete pier to keep debris from flying upward and onto the new eastern bridge next door.

Caltrans says the detonation registered 2.2 on the Richter scale. The implosion cost $20 million dollars.

Before the blast, the CHP halted traffic on the eastern span of the bridge and Marine units kept boaters 1,500 away from the blast site.

Seconds before the underwater explosives were set off, a bubble shield was created to protect fish and wildlife in the area.

There was also a floating sonar system, pinging sounds repel animals from the area.

The implosion was largely underwater. Spectators saw little other than a blast of water heaved 100 feet into the air.

Spectators like Jerry Le got up early to watch the blast from Treasure Island.

"I'm glad part of this historical event," said Le.

But not everybody was impressed.

"It was disappointing. We stayed up all night and got a little dud!" said Chance Johns, a San Francisco resident.

The bridge was completed in 1936, but its eastern span was badly damaged by the 1989 Loma Prieta earthquake. It was replaced in 2013.

The six-second blast was scheduled to take advantage of slack tide and light traffic on the new bridge, which was shut down for five to 15 minutes during the operation. Traffic was re-opened by 7:20 a.m.

There are 20 more piers that need to removed. Caltrans is currently deciding how to proceed.

The Associated Press contributed to this report.