As NBC Bay Area’s Investigative Unit has learned, the designer of the problematic repairs to the sinking and tipping Millennium Tower recently informed city officials about a particularly unpleasant potential byproduct of subdivision development – sewage backups.
“Sewer lines must have a slope (at least 1/8 inch per foot) to allow for efficient flow of material,” Ron Hamburger said in an email to city officials in late August. He identified at-risk drains that currently slope south and east — contrary to the current northwest slope — and said those lines “will experience a reduced gradient and potentially become a problem.”
The sewer alarm was part of an assessment of the building’s “functionality” as the building leaned an additional five inches during work on the so-called rehabilitation that began in May. This project is currently on hold pending testing and analysis, which triggered the unexpected, accelerated settlement.
Hamburger told city officials that experts were assessing the stress on vertical pipes due to the tilt, while engineers had found no signs of a “malfunction” in the elevator system.
With the building now tilted 22 inches to the west, experts believe the sewage problem will worsen because the tilt has flattened the angle of some drain lines by up to 25 percent.
The drains in the owner’s third-floor eat-in kitchen have already experienced “some blockages,” Hamburger said in his email summary to city officials, and they now require “maintenance through regular chemical flushing.”
“This and other lines may need to be adjusted to restore the grade,” Hamburger noted in a presentation to city officials.
“There is the problem that the slope is not enough or is too great, in either case there can be problems,” says Mark Savel, an architect and contractor with three decades of experience analyzing building damage, such as the balcony collapse in Berkeley in 2015.
“A blockage or system backup is to be expected – so the existing system should be inspected and monitored,” says Savel.
Meanwhile, residents risk losing entire wooden floors and walls because of the health risks associated with massive traffic jams, Savel says. He adds that the risk is particularly high when people use the system at the same time.
“On those days when the house is full of people, you’re celebrating a holiday, or you have a special occasion,” he says, “you end up calling Roto-Rooter. Because your system will be put to the ultimate test.”
Savel says building managers should first order a video inspection of all plumbing to identify immediate risks and long-term problems.
Any final solution, which would involve adjusting the height of hundreds of pipes to allow proper flow, would have to wait for the sinking and tilting structure to fully stabilize, he says.
