The Millennium Tower may be San Francisco's most famous tilting and sinking structure, but it is not the city’s only sinking problem.
Many streets in the city’s new Mission Bay neighborhood have started to sink, prompting worried officials to say that they will inspect the area as soon as next month, an NBC Bay Area investigation has found. They say the problem is more than an eyesore because people can trip over cracked, uneven sidwalks.
A brick monument that marks the entrance to the University of California, San Francisco's Medical Center is also symbolic of the bizarre phenomenon that is plaguing this newly constructed high-tech community — the streets and sidewalks are sinking around its gleaming structures.
At the base of the campus monument sign, it is evident that yellow bricks have sunk around the structure, which itself is supported by piles driven into the soft soil.
Other walkways are buckling nearby, some breaking away from the steel, glass and concrete structures that line the streets.
But Larry Karp, a veteran geotechnical engineer, has deemed the headache perfectly predictable.
“It’s going to go on and on and on – it’s not going to stop,” Karp says, explaining that it is a product of the weight of the streets and paved areas pressing down on soft, settling soil.
The problem is that the new Mission Bay community, comprising homes and a high-tech campus, sits atop land that was once known as Mission Swamp.
That swamp first became clogged by mining silt that washed down from the Gold Rush, Karp told us. It was topped with sand and debris from the 1906 earthquake so it could serve as a giant rail yard.
Today, as the reclaimed swamp is settling and giving way, crews are forced to make constant repairs at the UCSF campus and elsewhere.
Perhaps the most glaring evidence of the settlement is on the 1200 block of Fourth Street, where a residential and commercial building is supported on foundation piles, but the sidewalk around it has sunk as much as six inches.
City officials, alerted to the problem by NBC Bay Area’s investigative unit, recently marked the problem areas with white paint and gave the owner 30 days to come up with a fix.
“The sidewalk is not up to standard now because it is separating from the building itself,” said Jerry Sanguinetti, the chief of street use for San Francisco’s Department of Public Works.
Sanguinetti said the sinking was to be expected because of the soft, moist ground. That’s why the buildings are supported on piles driven into dense sand. He said the developers should have made sure the sidewalks were reinforced as well.
While merchants were reluctant to go on camera to talk about the problem, no one can escape the evidence of the problem.
The owner of a cafe on Fourth Street has marked the sagging sidewalk with yellow warning tape. Inspectors have flagged the hazard by spray-painting dots onto the fractured cement.
Across the street, a furniture store owner has to rely on a makeshift ramp so customers can safely access his showroom.
The ramp was put in three years ago. Already, the sinking means the structure needs to be raised.
One day after being approached by NBC Bay Area, officials with the Department of Public Works inspected both the café and furniture store.
"We found out because of this inquiry, so we decided that we should go out and treat your inquiry as a potential trip and fall hazard," and so they did, Sanguinetti said.
As a result, the city issued a 30-day repair notice to the owner of the furniture store building.
The building owner representative declined to comment.
According to Sanguinetti, the owner had already applied for approval on a plan to fix the problem when the notice was issued.
“I understand it was in parallel,” he said. “So as we were going out, they were already applying for a permit. ... My engineering staff was working on plans with them on how to mitigate the issue.”
Sanguinetti said the building's developer should have accounted for the potential of sinking during the planning phase of the project.
“What they need do is go in and basically re-structure those sidewalks to build them up to the standard that they should have done initially,” he said.
The builder of the community, Mission Bay Development Group, did not respond to NBC Bay Area's requests for comment.
Meanwhile, San Francisco officials plan to inspect 16 blocks of the development early next year, hoping that owners will act quickly to fix the problems.
“We can’t have people, you know, lollygagging, when we need to get this done,” Sanguinetti said.
But, Karp said that often trying to cure the sinking can make matters worse.
Layering concrete atop sagging pavement, just adds weight and contributes to more sinking, he said.
“They keep patching it, and it keeps adding to the load and it keeps going down,” he told us. “So, it’s part of life. You could live in Kansas — if you wanted to.”
Editor's Note: An earlier version of this story reported that the buildings are supported on “piles driven into rock.” Geotechnical experts have since clarified that the buildings are supported on “piles driven into dense sand.” We have changed the story accordingly.