Here's why water is seeping into bore of Caldecott Tunnel

Concerns about the structural integrity of the Caldecott Tunnel system have emerged due to a mystery surrounding water flowing through one of its bores.

Motorists on the eastbound side of the Caldecott Tunnel may notice wet roads in the first bore. However, an electronic sign placed before the tunnel warns of the presence of water.

A small amount of water has been discovered in the second bore of the Caldecott Tunnel, which also runs eastbound.

NextDoor, a social media platform for homeowners and residents, was lit up for days with comments and concerns.

"What's with Bore #1 of the Caldecott? We have not seen rain in a couple of weeks, but the water is on the roadway on the western end of the tunnel. What gives? Leaks presage structural damage, but what do I know?" one posting read.

Caltrans explained that the water in the tunnel is runoff from previous rains.

"The water is basically seepage, which is runoff from the rain we continually had earlier this year, and this is the water coming down from the hillside," said Caltrans spokesperson Bart Ney.

Though the Bay Area has not had heavy rainfall in a while, a significant amount of water from previous rains is coming from the hills above the Caldecott Tunnel.

Caltrans has embarked on a project to fix it.

The transportation agency said there is no leakage in the tunnel's fire control system or any other problems that would cause the issue, only the relentless flow of runoff. The water is properly flowing down into the drainage system, but the aging drains are overwhelmed by the flow.

"They're just so significantly clogged that we're going to have to do something a little more robust," said Ney.

As early as next week, Caltrans will deploy water jets at night to clean out debris and calcium buildup.