Caltrans Director Malcolm Dougherty said that while a completely watertight bridge is impossible, the degree of infiltration is a serious dilemma.

“We need to protect this. We need to come up with a solution,” he said.

The massive threaded rods are up to 24 feet long and two to three inches thick and keep the bridge from bucking off its bearings in the event of a quake.

Previous vulnerabilities were discovered 2 years ago when workers found that 32 steel bolts intended to stabilize the structure during an earthquake were brittle and cracked because the steel had been contaminated by hydrogen, either during manufacturing or from being left in holes that filled up with rainwater. It cost Caltrans millions of dollars to put protective metal saddles over the bolts.

It is critical to remedy the bridges defects because the structure connects two major fault lines, the San Andreas and Hayward faults.

“The city is going to need this bridge after a big event, because a bid even will bring San Francisco to its knees,” said Brian Maroney, the bridges chief engineer.

Sources: Discovery News, Wired