An estimated 20,000 vehicles a day pass through the Castillo Street interchange under and near Highway 101, an area that is consistently plagued by standing water and pavement problems.

Now, the agency that owns the interchange is working on a solution, albeit a temporary one, that it hopes will help solve the road’s issues.

The underpass was built in 1960, but damage from an earthquake in the area in 1971 created large cracks in the slabs of concrete that make up the roadway, said David Beard, project manager for Caltrans, which owns that section of road.

“That’s one of the major reasons it’s leaking,” he said. Though the slabs have been sealed and resealed from the damage, “we don’t really see that it can be stopped.”

Another problem is the area’s topography.

Beard estimates that portion of the street sits about 10 feet below the water table, and underground water consistently floods the area.

Caltrans examined the cost to fully replace the slabs years ago, and $25 million was the amount estimated to remedy the problems.

The project was tabled due to lack of funding, and “would likely be much more now with all the time that has passed,” Beard said.

In addition to the cost, there’s also the disruption to traffic that would occur. The area and interchange would have to be closed for up to a year as the work proceeded.

“It’s hard to make that work for everybody,” Beard said, adding that Caltrans has started to look at some short-term fixes to address the problems, including revisiting some past approaches.

In the late 1990s, Caltrans put in some interlocking concrete pavers in the area that worked well for four or five years before they started to deteriorate.

“It was just what it was supposed to be — a short-term fix,” he said.

The agency has even tried more high-tech approaches, such as using electrical pulses underground to keep water out, but it’s consistently been a problem, he said.

The pavers most likely will be the way forward for Caltrans, and Beard said construction would begin on the project in the spring of 2015 at the earliest. The pavers would last four or five years, but could be repeated and improved upon.

While the design will probably be similar to the pavers installed initially, “we’d like to find something that works as well or better” to drain water off the pavement surface, he said.

The prior design had pavers spanning under the highway and up to the railway bridge and up the highway ramps as well, he said.

That design would cost $400,000 to $500,000, and Caltrans should know in about six months which design it will be using.

Noozhawk staff writer Lara Cooper can be reached at Follow Noozhawk on Twitter: @noozhawk, @NoozhawkNews and @NoozhawkBiz. Connect with Noozhawk on Facebook.

— Noozhawk staff writer Lara Cooper can be reached at Follow Noozhawk on Twitter: @noozhawk, @NoozhawkNews and @NoozhawkBiz. Connect with Noozhawk on Facebook.